Abutment screw torque changes with straight and angled screw-access channels

doi:10.1016/j.prosdent.2020.01.018

The Journal of Prosthetic Dentistry

Volume 125, Issue 4, April 2021, Pages 675-681

Presented at the Graduate Student Research Competition (placed first) at the Annual Meeting of the Pacific Coast Society for Prosthodontics; Carlsbad, CA, June 2018

https://doi.org/10.1016/j.prosdent.2020.01.018 Get rights and content

Abstract

Statement of problem

Angle-correcting options allow the use of screw-retained implant prostheses in situations where an implant has been placed with a facial inclination. However, manufacturers have different recommended torque values, and it is unclear whether the performance of these designs is equivalent to that of the traditional screw-retained crowns (SRCs) when subjected to cyclic loading forces.

Purpose

The purpose of this in vitro study was to compare torque differences between conventional straight-line screw access and angulated access SRCs before and after simulated functional loading.

Material and methods

Five groups consisting of 10 SRCs and implants were formed: Nobel Biocare zirconia crowns with 20-degree access channels (NB-20); Dynamic Abutment Solution zirconia crowns (DA-20) with 20-degree access channels; Core3dcentre angle correction zirconia crowns with 20-degree access channels (C3D-20); Nobel Biocare zirconia crowns with 0-degree access channels (NB-0); and gold alloy crowns cast to Nobel Biocare Gold-Adapt abutments (GA-0). Each specimen underwent thermocycling before cyclic loading. A preload torque based on the manufacturer’s recommendation was applied to each crown placed on an implant. Reverse torque measurements were obtained for each specimen before cyclic loading. Each implant-abutment assembly was then cyclic loaded at 0 to 100 N at 10 Hz for 1 million cycles. Reverse torque measurements were obtained after cyclic loading and the percentage difference calculated.

Results

No significant percentage torque loss differences were observed between the 0-degree and 20-degree SRCs after cyclic loading. No significant differences were seen among the angulated access channel crowns. DA-20 and C3D-20 specimens had significantly higher torque loss compared with the NB-0 group. The C3D-20 group reported the largest percentage torque loss (34.5%) among the angulated access screw channel groups. The GA-0 group reported the largest percentage torque loss of all the groups (35.9%). No crown mobility or other complications were observed in any of the groups after cyclic loading.

Conclusions

Angulated access channel crowns performed comparably with conventional straight-line screw access SRCs with regard to percentage torque values after cyclic loading. Angulated access channel crowns with lower manufacturer recommended torque values had higher percentage torque differences.

Section snippets

Material and methods

Fifty implants (Nobel Biocare Replace Conical Connection 4.3×11.5 mm; Nobel Biocare AG) were embedded into chemically activated polymethyl methacrylate resin (Splint Acrylic Resin; Great Lakes Supply) exposing 2.0 mm of the implant platform.¹⁸ Each acrylic resin block was allowed to polymerize for 24 hours.

A wax pattern replicating a maxillary central incisor was scanned (3Shape 900L; 3Shape A/S) to create a standard tessellation language file for the standardized reproduction of all the crowns

Results

No significant difference (P=.154) was found in percentage change between initial and final screw torque values between the straight access channel groups and the angled access channel groups. There was a significant difference between NB-0 and DA-20 (P=.033), NB-0 and C3d-20 (P<.031), and NB-0 and GA-0 (P=.045), but no significant difference was found between NB-0 and NB-20 (P=.260). There was no significant difference between GA-0 and NB-20 (P=1.00), DA-20 (P=.872), or C3D-20 (P=.872). No

Discussion

The first null hypothesis was accepted as no significant difference was found in percentage change between initial and final screw torque values between the straight access channel groups and the angled access channel groups. Analysis among all the groups independently reported some significant differences in percentage torque values, and the second null hypothesis was rejected.

Few studies have compared the effects of the off-angle application of torque to modified abutment screws to those used

Conclusions

Based on the findings of this in vitro study, the following conclusions were drawn:

1.
Angulated access channel crowns perform comparably with straight-line screw access screw-retained crowns with regard to percentage torque values after cyclic loading.
2.
Angulated access channel crowns that have lower manufacturer recommended torque value have higher percentage torque differences.
3.
The Gold-Adapt crowns, made from a gold alloy, demonstrated the greatest percentage torque loss when compared with all

Acknowledgments

The authors thank Nobel Biocare for donating their products related to this study and Loma Linda University Center for Dental Research for additional financial support. The authors thank Dr Udochukwu Oyoyo, MPH, for contributions as a statistical consultant.

References (29)

T.D. Taylor et al.
Twenty years of progress in implant prosthodontics
J Prosthet Dent
(2002)
K.S. Hebel et al.
Cement-retained versus screw-retained implant restorations: achieving optimal occlusion and esthetics in implant dentistry
J Prosthet Dent
(1997)
J.R. Agar et al.
Cement removal from restorations luted to titanium abutments with simulated subgingival margins
J Prosthet Dent
(1997)
C. Wadhwani et al.
Radiographic detection and characteristic patterns of residual excess cement associated with cement-retained implant restorations: a clinical report
J Prosthet Dent
(2012)
C. Wadhwani et al.
A descriptive study of the radiographic density of implant restorative cement
J Prosthet Dent
(2010)
S. Garcia-Gazaui et al.
Fabrication of a screw-retained restoration avoiding the facial access hole. A clinical report
J Prosthet Dent
(2015)
L.A. Lang et al.
Finite element analysis to determine preload
J Prosthet Dent
(2003)
J. Goldberg et al.
Removal torque and force to failure of non-axially tightened implant abutment screws
J Prosthet Dent
(2019)
D.S. Palmer et al.
Temperature extremes produced orally by hot and cold liquids
J Prosthet Dent
(1992)
D.L. Dixon et al.
Comparison of screw loosening rotation, and deflection among three implant designs
J Prosthet Dent
(1995)

A. Khraisat et al.

Effect of lateral cyclic loading on abutment screw loosening of an external hexagon implant system

J Prosthet Dent

(2004)

K.X. Michalakis et al.

Cement-retained versus screw-retained implant restorations: a critical review

Int J Oral Maxillofac Implants

(2003)

S. Lewis et al.

The “UCLA” abutment

Int J Oral Maxillofac Implants

(1988)

W. Chee et al.

Screw versus cemented implant supported restorations

Br Dent J

(2006)

Cited by (19)

Effects of cyclic loading on loss of abutment screw torque of angled screw channel single implant crowns on narrow diameter implants
2023, Journal of Prosthetic Dentistry
Screw access channels that emerge on the facial aspect of anterior screw-retained implant crowns can compromise esthetics. Recently, angled screw channels (ASCs) have been developed that can alter screw access channel angulations to improve esthetics. While ASCs can be used on narrow-diameter implants, information is limited on the loss of abutment screw torque on narrow-diameter implants with ASCs.
The purpose of this in vitro study was to compare the loss of abutment screw torque after thermocycling and the cyclic loading of ASCs from 3 different companies connected to narrow-diameter implants.
A total of 40 narrow-diameter implants (NobelReplace Conical Connection 3.5×11.5 mm) were mounted individually in acrylic resin blocks and divided equally into 4 groups. The first group, NB-0 (Control), consisted of screw-retained zirconia crowns fabricated on ASCs at 0-degree angulation (n=10). The other 3 groups consisted of a total of 30 screw-retained zirconia crowns fabricated on ASCs at 20-degree angulation: NB-20 (Angulated Screw Channel Solutions), ATL-20 (Atlantis Custom Base Solution with angulated screw access), and DA-20 (Dynamic TiBase). Each crown was secured on the mounted implant with its corresponding titanium base insert and screw and then tightened to the manufacturer’s recommended torque with a digital torque gauge. The initial reverse torque value (RTV_I) was obtained and recorded at baseline. Subsequently, a new set of screws were tightened to recommended values, and each specimen underwent thermocycling and then cyclic loading at 0 to 100 N at 10 Hz for 1 million cycles to simulate 1 year of functional loading. After cyclic loading, the final reverse torque values (RTV_F) were recorded and compared with the RTV_I to evaluate the percentage torque loss (PTL_F). Statistical analysis was performed using the Kruskal-Wallis analysis, Rank base analysis of covariance (ANCOVA), and the Tukey HSD post hoc comparisons (α=.05).
Significant differences were found for the PTL_F among all groups after cyclic loading (P<.001). The PTL_F in ATL-20 (51.4%) was significantly higher than in NB-0 (22.2%) (P<.001) and NB-20 (29.2%) (P=.010). No significant difference was found in the PTL_F among other groups (P>.05).
The abutment screw torque loss after cyclic loading of the ASCs on narrow diameter implants among the 4 groups did not perform comparably. The largest percentage torque loss was recorded for the ATL-20 group. The NB-20 group demonstrated the lowest percentage torque loss. DA-20 showed percentage torque loss less than ATL-20; however, its RTV_F was the lowest.
Clinical performance of posterior monolithic zirconia implant-supported fixed dental prostheses with angulated screw channels: A 3-year prospective cohort study
2023, Journal of Prosthetic Dentistry
Citation Excerpt :
The fracture of the veneer material has been reported to be the most frequent complication, although it was not common in the present study.20 Recent in vitro studies have not found a significant difference in percentage change between initial and final screw torque values between the straight access channel groups and the angled access channel groups.26,27 Therefore, excessive occlusal loads and insufficient application of adequate torque during prosthetic placement are the possible reasons for screw loosening as reported for straight screw-retained FDPs.22,23,28
The choice of retention type of an implant-supported fixed dental prosthesis (FDP) becomes critical when the dental implant is not placed in a prosthetically ideal location. In recent years, computer-aided design and computer-aided manufacturing (CAD-CAM) technology has enabled the correction of the location of screw access hole depending on the clinical needs of the patient. However, how FPDs with angulated screw channels (ASCs) perform clinically is unclear.
The purpose of this prospective clinical study was to evaluate the mechanical complications and crestal bone loss (CBL) when posterior monolithic zirconia implant-supported FDPs with an ASC are used.
Participants (N=37) with a missing single posterior tooth or multiple teeth, sufficient bone height, and an implant site without infection were included. Each participant received parallel-walled implants (Nobel Parallel CC) of 7-, 8.5-, or 10-mm length by using a 1-stage approach. After 4 months of healing, a conventional impression was made, and a digital workflow was followed. Monolithic zirconia restorations (Katana ML) were milled, stained, and mechanically attached to a titanium base (NobelProcera ASC abutment). CBL was measured from radiographs at 6, 12, 24, and 36 months after the placement of the prosthesis. Implant and prosthetic characteristics including implant diameter, implant length, screw channel angle (angle≤15 degrees versus angle>16 degrees), prosthetic type (single crown versus multiple-unit FDP), and antagonist dentition (natural versus prosthesis) were also recorded. A generalized linear mixed model with a log link was estimated to assess the independent predictors of CBL among the angles of ASC-retained definitive restorations and the clinically relevant variables (α=.05).
Thirty-seven participants received 51 implants, and the median follow-up period was 30 months (interquartile range: 22-36). Two single-crown implants failed within the first 12 months of delivery. The implant and restoration survival rate was 96% at 36 months. Screw loosening was recorded in 2 study participants. After a follow-up of 36 months, the mean ±standard deviation CBL value was 0.15 ±0.14 mm with an increase over time (P<.001). The effect of the angle of ASC, implant diameter, implant length, prosthetic type, and antagonist on the CBL was not statistically significant (P>.05).
CBL was not associated with the angle of ASC, implant diameter, implant length, prosthetic type, or antagonist when posterior monolithic zirconia implant-supported FDPs with ASCs were used. Screw loosening in 2 situations was the only mechanical complication during the first 3 years of service.
A method of removing the stripped abutment screw from the angled screw channel: Technical details and a clinical report
2023, Journal of Prosthetic Dentistry
An angled screw channel (ASC) avoids a facial screw hole by correcting the pathway of the screwdriver. However, the structure of the specially designed screw is prone to mechanical complications, including screw-head stripping. Removing an angled screw is challenging because regular screw-removal tools cannot access the ASC. A safe and convenient method for the retrieval of the stripped screw is reported.
Effect of cyclic loading on reverse torque values of angled screw channel systems
2022, Journal of Prosthetic Dentistry
The angled screw channel concept has become popular. However, research is lacking as to how reverse torque values of nonaxially tightened implant crowns compare with axially tightened cement-retained crowns restored on angle-correcting abutments when subjected to long-term cyclic loading.
The purpose of this in vitro study was to evaluate the ability of different 25-degree angled screw channel hexalobular systems to apply the target torque value on their screws, the effect of cyclic loading on their reverse torque values, and their survival compared with crowns cemented on conventional 0-degree screw channel abutments.
A total of 28 implants were divided into 4 groups. Twenty-one angled screw channel crowns were fabricated at a 25-degree angle correction by using angled titanium (Ti) bases by 3 manufacturers DY (Dynamic Tibase), DE (AngleBase), and ASC (Angulated Screw Channel) (n=7). The fourth group, UB (Universal Base, Control), had cement-retained crowns with 25-degree custom-milled, angled zirconia abutments that were cemented onto their respective Ti bases (n=7). All implants were embedded in epoxy resin blocks and tightened to manufacturer recommended values: 35 Ncm for ASC, UB, and DE and 25 Ncm for DY. Initial torque values (ITV1) were recorded. After 24 hours, the reverse torque values (24hr-RTV1) were recorded. A new set of screws was then used for each group, and the initial torque values (ITV2) were recorded. Specimens were loaded at 2 Hz for 5 million cycles under a 200-N load, and reverse torque values (RTV2) were recorded. ANOVA (α=.05) was used to compare differences in the means of deviation of initial torque values and means of reverse torque values followed by a Tukey-Kramer post hoc analysis (α=.05). Preload efficiency was calculated for each system (RTV2/ITV2), and a survival analysis was performed by using the Lifetest procedure.
A significant difference in the means of deviation of initial torque values of the groups with 25-degree torque application (DY, DE, and ASC) was found when compared with UB at 0 degrees. ASC and DE had lower initial torque values than UB (P<.001 and P=.003 for ASC ITV1 and ITV2, P<.001 and P=.006 for DE ITV1 and ITV2). A significant difference was found in mean reverse torque values both for after 24 hours and after cyclic loading among all groups (P<.001). A significant difference was found between mean reverse torque values before and after cyclic loading for each group (P<.001). Preload efficiency was 43.8% for DY, 46.8% for DE, 54.2% for ASC, and 48.5% for UB. No significant difference was found in the time-to-failure survival among groups (P>.05).
The hexalobular system of DY delivered comparable initial torque values to its target value at 25 degrees, similar to how UB (control group) delivered at 0 degrees. ASC and DE scored lower initial torque values than their target value compared with UB. The DY abutment, which had a lower manufacturer recommended torque value, had lower reverse torque values compared with those of other groups. Time-to-failure survival of all groups was similar. Fractures at the zirconia to titanium base connection were seen with ASC crowns.
The ability to screw-retain single implant-supported restorations in the anterior maxilla: A CBCT analysis
2022, Journal of Prosthetic Dentistry
Citation Excerpt :
Both groups reported statistically significant differences in the reverse torque values between the differing angulations, with the 20- and 28-degree groups exhibiting more change than the 0- or 10-degree channel groups. When cyclical loading was incorporated in the study model, no significant percentage torque loss differences were found between the 0- and 20-degree screw-retained crowns.32 Goldman et al33 reported no differences between torque removal values when a dynamic abutment screw was initially tightened to 25 Ncm in a 0-, 20-, or 28-degree screw channel.
Evidence to validate the routine use of angled screw-channel abutments in the anterior maxilla is sparse. If properly planned, they might provide surgical and prosthetic benefits.
The purpose of this observational study was to determine the prevalence of digitally placed implants in the anterior maxilla that would allow screw-retained implant-supported restorations with either a straight or an angled screw-channel abutment.
Two hundred cone beam computed tomography (CBCT) scans met the inclusion criteria for retrospective analysis and digital implant planning. Virtual implants were planned for randomly selected anterior maxillary teeth by using the anatomic crown and root position. Virtual abutments of varying angulation were attached to the implants to determine the ability to screw retain a restoration with either a straight or an angled screw-channel abutment.
One hundred fifty-two (76%) sites required an angled screw-channel abutment to enable screw retention. Forty-eight (24%) sites allowed screw retention with a straight abutment. The percentage of implants requiring angled or straight abutments varied significantly among anterior teeth (P<.005). One hundred nine (71.7%) angled screw-channel abutment sites required a 5-degree abutment, 41 (26.9%) required a 10-degree abutment, and 2 (1.3%) required a 15-degree abutment. Among the anterior teeth, lateral incisors presented a greater need for angled screw-channel abutments. None of the implants in the present study needed cement-retained restorations.
Angled abutments allowed for screw-retained restorations on digitally planned implants in the anterior maxilla. The required angular correction to a screw-retained restoration was ≤15 degrees. Screw-retained restorations were frequently achievable (76%) with the use of angled screw-channel abutments or with straight abutments (24%), and lateral incisors presented a greater need for angled screw-channel abutments.
Screw loosening in angulation-correcting single implant restorations: A systematic review of in vitro studies
2022, Journal of Prosthetic Dentistry
Citation Excerpt :
The reason for doing so is to introduce both the bending and compression forces a tilted implant would experience in vivo. The recommended loading angle was applied in the studies by Hotinski et al,25 Hein et al,12 Swamidass et al,24 and de Aguiar Vilela Junior et al.3 Much like a spring, metals have a physical stiffness (Young's modulus), which represents a metal’s ability to return to its original position after loading.28,29
Various options are available to allow angle correction for screw-retained restorations for malaligned implants, including angled abutments, angled screw channel abutments, and angled implants. However, the effect these angle correction components have on prosthetic screw loosening is unclear.
The purpose of this systematic review was to assess the effect of angled abutments, angled screw channel abutments, and angled implants on prosthetic screw loosening.
This manuscript followed the Preferred Reporting Items for the Systematic Review and Meta-Analyses (PRISMA) statement. Searches were performed through 31 December 2021 in PubMed/MEDLINE, EMBASE, and Web of Science with no year limit targeting in vitro studies evaluating the effect of angulation correction components on screw loosening.
A total of 460 articles were identified. After removing duplicates, 306 titles were screened. Nine of the remaining 36 articles selected for full-text analysis met the selection criteria. The qualitative analysis used data from 394 implants. All studies featured straight abutments as the control group, and, in 8 studies, the angle correction component was included on the level of the abutment. Only in 1 study was the angle correction component at the level of the implant. The angle correction of the prosthetic component varied from 0 degrees in all studies up to a maximum correction of 30 degrees. Statistically significant increases in screw loosening with increasing abutment angle correction were reported by multiple authors (P<.05). However, other articles reported nonsignificant differences in screw loosening because of angulation after cyclic loading (P>.05). The only study investigating angle correction at the implant level found significantly less screw loosening (P<.05) in the angled implant group compared with the nonangled implant group.
Several options are available to correct discrepancies between the surgical axis and the ideal prosthetic axis for rehabilitations supported by dental implants. The current evidence does not clearly indicate the superiority of any single solution for minimizing screw loosening.

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Research and EducationAbutment screw torque changes with straight and angled screw-access channels

Abstract

Statement of problem

Purpose

Material and methods

Results

Conclusions

Section snippets

Material and methods

Results

Discussion

Conclusions

Acknowledgments

J Prosthet Dent

J Prosthet Dent

J Prosthet Dent

J Prosthet Dent

J Prosthet Dent

J Prosthet Dent

J Prosthet Dent

J Prosthet Dent

J Prosthet Dent

J Prosthet Dent

J Prosthet Dent

Cement-retained versus screw-retained implant restorations: a critical review

Int J Oral Maxillofac Implants

The “UCLA” abutment

Int J Oral Maxillofac Implants

Screw versus cemented implant supported restorations

Br Dent J

Research and Education
Abutment screw torque changes with straight and angled screw-access channels