Screw Access Research Articles

Effect of screw access hole on the fracture load of implant-supported monolithic zirconia single crown

ABSTRACT Implant-supported cement–screw-retained crowns combine the advantages of screw-retained and cement-retained crowns. However, the occlusal screw access hole interrupts porcelain integrity, which may result in porcelain cracks or fractures. There is insufficient scientific evidence to prove that screw access holes affect the fracture load of implant-supported monolithic zirconia crowns. In this study, we investigated the effects of the screw access hole and its preparation technique on the fracture load of implant-supported monolithic zirconia single crown. The crowns were designed for the maxillary right first premolar. Three techniques analysed for screw access hole preparations included computer-aided designed/computer-aided manufactured (CAD/CAM) before sintering, manually prepared after sintering, and then resintering. Our findings show that the screw access holes and preparation techniques have no significant effects on the fracture load of implant-supported monolithic zirconia single crown. On the other hand, the screw access hole preparation techniques affect failure initiation in implant-supported monolithic zirconia single crown.

Visual inspection of implant screw access hole with an endoscope camera

Prosthetic complications may necessitate the removal of an implant-supported restoration.1-4 Retrieval of cement-retained implant prostheses without any preexisting index of the screw access hole is challenging as it requires precision from the clinician during attempts to locate the abutment screws.5,6 Implants placed in unfavorable positions make the visibility of the screw access hole difficult, and the retrieval attempts in such situations pose a threat to the implant components, the intaglio surface of the implant, or the abutment screw.

Challenges in Managing a Fractured Cement-retained Crown Located at the Aesthetic Zone: A Case Report

Implant prosthesis is a popular treatment modality but it is not complication free. This article discussed the management of a cemented, all-ceramic implant crown in the maxillary anterior region that had veneering ceramic fracture after three years in function. A screw-retained prosthesis was prescribed to avoid the show of the screw access channel on the incisal edge of the crown. This was achieved by changing the location of the screw hole using the angle screw channel that overcame the angulation issue.

Comparison of strength of milled and conventionally processed PMMA complete-arch implant-supported immediate interim fixed dental prostheses

Statement of problemA typical conversion process of a complete-arch immediate loading protocol entails preparing holes in a complete denture for connection to interim copings, which reduces the strength of the prosthesis. The excellent mechanical properties of milled polymethyl methacrylate (PMMA) disks may provide interim prostheses with improved strength. PurposeThe purpose of this in vitro study was to measure the flexural strength and failure load of simulated acrylic resin immediate implant-supported interim prostheses fabricated by conventional processing and computer-aided manufacturing. Material and methodsA master patient model was created with an acrylic resin base and 2 BioHorizons Internal 4.5-mm-diameter implants placed with a 21.5-mm span and multiunit abutments (MUA) tightened to place. Two groups with different prosthodontic designs were used: one represented the standard fixed prosthesis with support at each end (noncantilever, NC), and the other group represented the cantilever portion of the prosthesis (cantilever, C). Two connection designs of prosthesis blocks to MUA abutments were evaluated: one with typical holes in the prosthesis for capturing interim copings and one with a low-profile coping. For the heat-processed PMMA groups (HP/NC and HP/C), wax patterns were milled, and heat-polymerized denture base PMMA prostheses were processed. The milled PMMA groups (M/NC and M/C) were milled from a tooth-shaded PMMA disk for the prosthesis blocks. The milled low-profile groups (Mlp/NC and Mlp/C) had identical dimensions except that connection to the low-profile coping was designed with a cement space and a narrow diameter screw access hole and was milled from a PMMA disk. The failure load (N) of the cantilever prostheses was recorded, and for NC groups, the 3-point flexural strength formula (MPa) was calculated. The Weibull modulus, characteristic strength, and summary statistics were computed, and the groups were statistically analyzed with ANOVA and the post hoc Tukey test (α=.05). ResultsThe mean flexural strengths (MPa) were HP/NC=91.35 ±18.92; M/NC=143.94 ±36.79; Mlp/NC=117.06 ±13.86. Significant differences were found among groups (P<.001). Mean failure loads (N) and Weibull modulus (WM) of cantilever prosthesis strengths were for HP/C=512.66, WM=5.597; M/C=695.06, WM=4.875; Mlp/C=254.97, WM=1.797 (P<.001). ConclusionsImplant fixed interim structures milled from high-density PMMA blanks had a 35% higher flexural strength for both the standard prostheses and the cantilever prostheses than heat-processed denture base PMMA. The low-profile coping design was stronger than the heat-processed material, and the failure point was relocated from the lateral walls to the cervical margin area.

A Special Design to Facilitate Retrieval of Cement-Retained Zirconia-Based Implant-Supported Restorations.

Statement of the Problem: Retrieval of cement-retained implant-supported restorations is challenging in cases of screw loosening or periodontal problems.Purpose: The purpose of this study was to evaluate the effect of the screw access hole on the fracture resistance of zirconia-based cement-retained restorations with and without an access opening.Materials and Method: In this in vitro study thirty-three cement-retained implant-supported zirconia-based molar crowns were fabricated and divided into 3 groups (n=11). As the control group, group 1 consisted of conventional cement-retained crowns. Group 2 comprised conventional cement-retained crowns in which a hole was created in the location of the screw. Group 3 consisted of cement-retained crowns in which a ledge was created in the location of the screw access channel. The specimens were cemented to their abutments and their access openings were filled with composite resin. A compressive load was applied to the specimens using a universal testing machine until they fractured. The mean fracture resistance values of the samples were compared by using the one-way ANOVA and Tamhane post-hoc test (a=0.05).Results: The mean fracture resistance values were 1270.18± 12.67 N in group 1 (the control group), 960.09±210.67 N in group 2 (conventional), and 1357.81±361.68 N in group 3 (the special design). The fracture resistance value was higher in the special design group than that of the conventional design (p= 0.018) and the fracture resistance value of the conventional design group was less than that of the control group (p= 0.042). No statistically significant difference was detected between the control group and the special design group in fracture resistance values.Conclusion: Preparing a screw access hole in cement-retained implant-supported zirconia-based crowns decreased the fracture resistance of the restoration. Designing a ledge in the zirconia framework around the access hole may increase the fracture resistance of the restoration.

Framework Fracture of Zirconia Supported Full Arch Implant Rehabilitation: A Retrospective Evaluation of Cantilever Length and Distal Cross-Sectional Connection Area in 140 Patients Over an Up-To-7 Year Follow-Up Period.

To evaluate the relationship between different dimensional parameters in implant-supported monolithic zirconia fixed complete dental prostheses (IFCDPs) and the incidence of framework fracture in a large sample of cases in vivo. This retrospective observational study evaluated all patients rehabilitated with screw-retained zirconia IFCDPs between January 2013 and April 2019 at a private practice. The minimum follow-up period was 1 year after occlusal loading. Fractures were classified as: type I-fractures that happened between but not involving the two most posterior screw-access openings (SAOs) and type II-fractures of the distal cantilever. Cantilever length, distal connector cross-sectional area, and screw access opening length were measured using data obtained from digital scans. Logistic regression was performed to evaluate the relationship between types I and II fractures and the independent variables (dimensional parameters). Using the receiver operating characteristic curves, two parameters were identified to be useful for establishing a cut-off and predicting type II fractures. A total of 180 prostheses delivered to 140 patients were analyzed. Five implants failed in three patients: three before delivery of the definitive prostheses and two after. Ten prostheses failed (5.6% prosthetic failure rate): 2 because of implant failures, and 8 because of framework fractures. Five fractures were classified as type I and three as type II. Significant associations were found between cantilever length and type I fractures (Wald = 5.772, df = 1, p = 0.016), distal connector cross-sectional area and type II fractures (Wald = 3.806, df = 1, p = 0.051), and cantilever length and the total number of fractures (Wald = 6.117, df = 1, p = 0.013). Zirconia IFCDPs may be reliable medium-term solutions if some dimensional parameters are followed. The ratios between the cantilever length and cross-sectional connector area should be <0.51, while the ratio between the cantilever length and screw access opening length should be <1.48.

Implant repositioning with segmental osteotomy

IntroductionThe aim of this study is to assess a pioneering technique for atrophic premaxilla restoration. The objective is to reposition an implant reconstruction zone into a position both anatomically and physiologically suitable for occlusal function. Indeed, unlike the other few articles published on the correctional osteotomy of the implant in an inadequate situation, we have planned here an initially «unsuitable» insertion in order to benefit of the available bone mass. Material and method3 patients aged 14–20 years old (1 woman and 2 men) were operated on at the maxillo-facial department of Lille 2 University Hospital for partial implant-prosthetic rehabilitation on atrophic maxillary and/or mandibular sector.13 implants were seated (85% in the maxilla) in the native bone then moved subsequently by segmental osteotomy. ResultsThe patients were assessed both clinically and radiologically according to the functional and aesthetic criteria of implant-prosthetic restoration.Functionally, a biomechanically favourable implant/number of teeth ratio (80%) was achieved, with consistent occlusal relationships (centric positioning of the midline point and absence of crossbite) in 100% of cases. Aesthetically, the screw access hole is systematically non-apparent (100%) but has a prosthetically substituted reduced gingivo-alveolar architecture. DiscussionThese observations suggest that implant repositioning with segmental osteotomy allows for atrophic premaxilla restoration in implanted bone volume whatever the initial angulation.Peri-implant aesthetic difficulties are not specific to the technique suggested here but are quite common to all premaxilla reconstruction techniques.Lastly, this group of three patients is not enough to be conclusive, and a larger group would be necessary to validate this type of management.

Fracture resistance of cement-retained and screw-cement–retained milled posterior crowns with screw-access hole preparations before and after firing: An in vitro study

Statement of problemWhen a cement-retained lithium disilicate crown needs to be removed, perforation is needed to reach the abutment screw. How this process affects its strength is unclear. PurposeThe purpose of this in vitro study was to evaluate the fracture strength of milled lithium disilicate implant crowns with screw-access holes created before and after the firing stages. Material and methodsNine implant replicas with stock abutments were embedded in acrylic resin. Forty-five lithium disilicate (IPS e.max CAD) crowns were designed, milled, and divided into groups. The control group had no screw access, the blue state group had the screw access created in the intermediate phase of the ceramic, and the postfiring group had the screw access created after firing. The crowns were cemented with a self-adhesive resin cement, placed in an incubator for 24 hours and then thermocycled. The screw-access holes were sealed with composite resin. The crowns were loaded to failure with a universal testing machine using a 1- mm-diameter ball at a crosshead speed of 0.5 mm/min and a 5-kN cell load. Data were analyzed by ANOVA and the Tukey post hoc test (α=.05). ResultsScrew-access holes created before and after firing stages had a significant effect on the fracture resistance of lithium disilicate crowns (P=.002). No difference in fracture resistance was observed between the control group and the blue state group (P>.05), while the fracture resistance of the postfiring group was significantly lower than that of the control group and the blue state group (P<.05). ConclusionsThe fracture strength of lithium disilicate crowns was not affected by a screw-access hole created during the blue state of the ceramic followed by repair with composite resin. Creating a screw-access hole after firing the ceramic reduced fracture strength.

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.

Influence of Cyclic Loading on Load to Failure of Different Ceramic CAD/CAM Implant-Supported Single Crowns

To compare the load to failure values of different ceramic CAD/CAM implant crown materials with drilled screw access holes with and without cyclic loading applied. Forty zirconia abutments with a titanium base were pre-loaded onto implants to support maxillary right first premolar crowns that were milled from four different CAD/CAM ceramic materials (zirconia reinforced lithium silicate, hybrid ceramic, lithium disilicate, and zirconia; n = 10 each). After cementing the crowns, screw access channels were prepared by drilling through occlusal surfaces. Half of the specimens were subjected to cyclic loading for 5 million cycles at 2 Hz (n = 5/material). After cyclic loading, vertical loads were applied to failure, and the load to failure values of all crowns were recorded and statistically analyzed. Two-way analysis of variance was used with restricted maximum likelihood estimation and Tukey-Kramer adjustments (α = .05). During cyclic loading, the zirconia abutment in one lithium disilicate specimen cracked at 2 million cycles, as well as a zirconia-reinforced lithium silicate crown. Results for the load to failure test series showed statistical differences between the materials. Zirconia resulted in significantly higher failure loads when compared to the other materials (P < .001). Cyclic loading did not significantly affect the load to failure values. Cyclic loading did not significantly influence the load to failure of any of the materials tested. Zirconia crowns with drilled screw access channels cemented on zirconia abutments with a titanium base had higher load to failure values compared to the other ceramic crown materials.

Abutment Screw Loosening in Single Implant Restorations: Evaluation of Fracture Strength of Implant-Supported Cement-Retained Monolithic Zirconia Restorations Repaired with Porcelain and Composite Resin

Aim: To assess the fracture strength of repaired implant-supported cement-retained monolithic zirconia restorations with porcelain and composite resin. Materials and methods: Nighty monolithic zirconia crowns were cemented over the implant abutments, and divided into three groups (n = 30): control, screw access hole preparation in the crown and its restoration with composite resin (HC), and screw access hole preparation in the crown and its restoration with feldspathic porcelain (HP). Fracture strength was measured by a universal testing machine. Data were analyzed (α 0.05). Conclusion: Repaired implant-supported monolithic zirconia crowns with feldspathic porcelain provided a fracture strength comparable to that in the control group.

Effect of screw access channel on the fracture rate of lithium disilicate cement-retained implant-supported posterior crowns

Statement of problemWhether the presence of a screw access channel on the occlusal surface of a lithium disilicate cement-retained single tooth implant restoration reduces its fracture rate is unclear. PurposeThe purpose of this randomized controlled clinical trial was to compare the fracture rate of lithium disilicate cement-retained posterior single tooth implant restorations with or without screw access channels. The study also evaluated whether the crown dimensions and location of the occlusal screw access channel would affect the fracture rate. Material and methodsA split-mouth study was conducted where 40 participants having 2 implants placed to restore single missing posterior teeth with crowns were enrolled. Implants were randomly allocated into a conventional crown group or a screw access group, receiving cement-retained restorations fabricated from lithium disilicate glass-ceramic with and without an occlusal screw access channel. Crown dimensions were recorded in millimeters from the designing software program. Follow-up evaluations were made at 3, 6, and 12 months by observing visible cracks or fractures of the crowns. The Kolmogorov-Smirnov test of normality was used. Comparisons were carried out by using the Student and Welch t tests (α=.05). ResultsAfter a 12-month follow-up period, no crowns fractured or revealed visible cracks, resulting in a 100% success rate. No statistically significant differences were found between the conventional crown group and screw access channel group in all crown dimensions (P>.05). ConclusionsThe presence of an occlusal screw access channel did not affect the short-term fracture rate of lithium disilicate cement-retained single implant–supported posterior crowns. The amount of axial cantilever, occlusal ceramic thickness, and location of the screw access channel on the occlusal surface of the restoration have no effect on its fracture rate.

The Use of Angulated Screw Channel Abutment System for Anterior Single-Implant Restorations: A Clinical Report

The purpose of this clinical report is to explain the use and advantages of hybrid abutment crowns supported by ti-base abutments with Angulated Screw Channel (ASC) for anterior single-implant restorations. ASC system abutments have recently released to market as a solution of visible screw access problem in the esthetic zone. Moreover, using hybrid abutment consists of ti-base abutment with ASC system and esthetic materials may be a new method to combine esthetic and mechanical strength advantages for anterior single implant restorations. The use of ASC system with hybrid abutment crown design may allow clinicians to obtain optimal esthetics and mechanical strength in the case of over-angulated implants.

Complications of Fixed Full-Arch Implant-Supported Metal-Ceramic Prostheses.

We aimed to assess the biological and mechanical-technical complications and survival rate of implants of full-arch metal-ceramic prostheses, during five years of follow-up. 558 implants (of three different brands) retaining 80 full-arch metal-ceramic prostheses were placed in 65 patients, all of whom were examined annually for biological and mechanical-technical complications during the five years of follow-up. Descriptive statistics and univariate logistic regression were calculated. The cumulative survival rate of the implants was 99.8%, and 98.8% prosthesis-based. Mucositis was the most frequent of the biological complications and peri-implantitis was recorded as 13.8% at restoration-level, 16.9% at patient level and 2.0% at implant level. An implant length greater than 10 mm was shown to be a protective factor against biological complications. The mechanical-technical complications were associated with implant diameter, abutment/implant connection and retention system. Loss of screw access filling was the most frequent prosthetic complication, followed by the fracture of the porcelain. Full-arch metal-ceramic prostheses show a high prevalence of implant and prosthesis survival, with few biological and mechanical-technical complications.

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

Statement of problemAngle-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. PurposeThe 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 methodsFive 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. ResultsNo 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. ConclusionsAngulated 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.

A straightforward approach to conservative screw access for implant-supported fixed complete dentures

For decades, implant-supported fixed complete dentures have been used successfully to restore the masticatory system of edentulous patients.1,2 Multiple combinations of materials are available for the fabrication of these prostheses, each with different clinical indications and physical properties.3 Fixed complete dentures have a long history of use1 and have been reported to protect the bone-to-implant interface because of the shock-absorbing properties of the acrylic resin covering the framework.

Survival Probability, Weibull Characteristics, Stress Distribution, and Fractographic Analysis of Polymer-Infiltrated Ceramic Network Restorations Cemented on a Chairside Titanium Base: An In Vitro and In Silico Study.

Different techniques are available to manufacture polymer-infiltrated ceramic restorations cemented on a chairside titanium base. To compare the influence of these techniques in the mechanical response, 75 implant-supported crowns were divided in three groups: CME (crown cemented on a mesostructure), a two-piece prosthetic solution consisting of a crown and hybrid abutment; MC (monolithic crown), a one-piece prosthetic solution consisting of a crown; and MP (monolithic crown with perforation), a one-piece prosthetic solution consisting of a crown with a screw access hole. All specimens were stepwise fatigued (50 N in each 20,000 cycles until 1200 N and 350,000 cycles). The failed crowns were inspected under scanning electron microscopy. The finite element method was applied to analyze mechanical behavior under 300 N axial load. Log-Rank (p = 0.17) and Wilcoxon (p = 0.11) tests revealed similar survival probability at 300 and 900 N. Higher stress concentration was observed in the crowns’ emergence profiles. The MP and CME techniques showed similar survival and can be applied to manufacture an implant-supported crown. In all groups, the stress concentration associated with fractographic analysis suggests that the region of the emergence profile should always be evaluated due to the high prevalence of failures in this area.

Comparison of Success Rates of Cone Beam Computed Tomography in the Retrieval of Metal-Ceramic vs All-Ceramic Implant-Supported Restorations: An In Vitro Study.

To assess the success rates of cone beam computed tomography (CBCT) in identifying the locations and directions of abutment screw access holes (ASAHs) in metal-ceramic and all-ceramic implant restorations. Thirty-two implants were inserted into four clear acrylic casts. Metal-ceramic and all-ceramic crowns were placed on the inserted implants in two successive tasks. A maxillofacial radiologist determined the locations and angles of the ASAHs based on the CBCT images that were taken from the casts. Locations obtained from the CBCT images were carefully transferred to the crowns as access points. A prosthodontist pierced the crowns along the proposed access points and in the direction determined based on the CBCT images. Proper crown removal was considered to be the mark of success of CBCT in detecting ASAH location and direction. Fisher exact and chi-square tests were used to compare the results between the two types of restoration. Success rates of CBCT for defining ASAH location and direction were, respectively, 96.9% and 93.8% in metal-ceramic restorations and 78.1% and 59.4% in all-ceramic restorations. There were no significant differences between the two restoration types regarding the detection of location in either molar (P = .333) or premolar (P = .226) crowns. Abutment angle did not affect the success rate of CBCT in determining ASAH location or direction in metal-ceramic restorations. CBCT images define the locations and directions of ASAHs in metal-ceramic restorations more reliably than in all-ceramic restorations. In contrast to the metal-ceramic crowns, the success rate of CBCT in all-ceramic crowns is more dependent on abutment angle and crown morphology.

Survival rates and prosthetic complications of implant fixed complete dental prostheses: An up to 5-year retrospective study

Statement of problemImplant fixed complete dental prostheses (IFCDPs) are widely used in the rehabilitation of completely edentulous patients, yet limited information is available on the relationship between prosthetic complications and patient-associated and prosthesis-associated risk factors. PurposeThe purpose of this retrospective study was to assess the prosthetic complication and survival rates of IFCDPs after a mean observational period of 3.5 years. Material and methodsEligible participants were identified by an electronic health record review. The study consisted of a review of the dental record and a single-visit study appointment when a comprehensive examination was performed, including a review of the medical and dental history, clinical and radiographic examination, intraoral photographs, patient satisfaction questionnaire, and occlusal analysis. Prosthodontic parameters and risk factors were assessed, including time with the prosthesis in place, bruxism, occlusal device use, prosthesis material, number of implants, cantilever length, and mode of prosthesis retention. Association between these prosthodontic parameters and risk factors and the observed prosthetic complications was assessed. ResultsA total of 37 participants (mean age 62.35 ±10.39 years) with 48 IFCDPs were included. Thirty-eight prostheses were metal-acrylic resin (MR group), whereas 10 were metal-ceramic (MC group). Five of the 48 prostheses failed during the follow-up period, a cumulative prosthesis survival rate of 88%. Minor complications were more frequent than major complications. The most frequent minor complication was loss of screw access hole material (5.18%/year), whereas the most frequently observed major complication was major wear of the prosthetic material (5.85%/year). A significant association was found between not wearing an occlusal device and minor chipping, loss of access hole material, and framework fracture. Minor chipping was significantly associated with bruxism, whereas the opposing dentition significantly affected the total number of prosthetic complications. ConclusionsHigh survival rates were observed with both MR and MC IFCDPs. No significant difference was found between MR and MC groups in terms of patient satisfaction, as well as total number of prosthetic complications.

Adhesion properties of modified cement-retained implant prostheses: In vitro mechanical tensile experiments and computational fluid dynamics analyses

Statement of problemThe adhesion properties of modified cement-retained implant prostheses have not been elucidated. PurposeThe purpose of this in vitro study was to compare the adhesion strength and the flow conditions of the adhesives of 3 common modified cement-retained methods (MCRMs). Material and methodsFour cement-retained methods were used: an occlusal hole for screw access (OH), a lingual hole for releasing the excess adhesive (LH), a resin replica for the titanium abutment (RR), and a control group (no holes and no resin trial abutments). Eight zirconia prostheses in each group were processed and cemented. The adhesion strength was examined by mechanical tensile experiments (MTE) in vitro. One-way ANOVA and the LSD post hoc tests were used to compare the results of the MTE (α=.05). The flow conditions of adhesives in the adhesion process were analyzed by computational fluid dynamics (CFD). CFD-Post 16.0 (ANSYS, Inc) was used to analyze the results of the CFD analyses. ResultsThe adhesion strength of each group was 289.3 ±37.7 N in the LH group, 281.3 ±50.1 N in the OH group, 263.3 ±49.3 N in the RR group, and 239.2 ±29.4 N in the control group. A statistically significant difference is seen in the adhesion strength between the LH group and the control group (P=.025). The internal filling ratio of adhesives between the groups ranges from high to low in the order the LH group, the OH group, the RR group, and the control group. The amount of cervical overflow of adhesives between the groups ranges from less to more in the order the RR group, the OH group, the LH group, and the control group. ConclusionsMCRMs can effectively reduce the amount of cervical overflow of adhesives and improve the filling condition of the adhesive and its clearance to ensure the adhesion strength of the prostheses.