Screw Access Research Articles

Effect of screw access channel filling materials on uniaxial retentive force of cement‐retained implant restorations

This study aimed to investigate the effect of various abutment screw access channel filling materials on the uniaxial retention of castings cemented onto the abutment using temporary cement. Ten straight, regular platform Esthetic Abutments were used. Fifty castings were divided into five groups and the abutment screw access channels were filled with composite resin (Filtek Z 250), light-cured temporary filling (Clip), temporary filling (Coltosol), polyvinyl siloxane impression material (Elite H-D), or polytetrafluoroethylene (PTFE) tape. Castings were cemented and thermal cycled. A uniaxial tensile force with a cross-head speed of 5 mm/min, was applied to the castings until cement failure occurred. One-way analysis of variance was used to perform intergroup comparisons of the mean uniaxial retentive force (URF) values and Tukey's HSD test was used to determine the group causing the difference. There were statistically significant differences between the mean URF values for the groups (p < 0.01). The mean URF value for the composite resin group was statistically higher than those for the other filling material groups respectively (p < 0.05). The retention of castings cemented to straight implant abutments using non-eugenol temporary cement may be influenced by the screw access channel filling material.

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.

Horizontal Denture: A Prosthodontic Alternative for Severe Maxillary Atrophy

Horizontal Denture: A Prosthodontic Alternative for Severe Maxillary Atrophy

Demystifying the Retrievability of Cement-retained Implant-supported Restorations

The field of impla nt prostheses has come of age in the postBranemark era. Various research studies are being carried out world over, in order to formulate superior materials, achieve better esthetic outcomes, quicker functional results, minimal treat ment complications and maximal comfort to the patient in concern. Prost hetic reconstruction involving implants may involve screw-retained or cement-retained crowns depending upon the clinician’s preference and the clinical situation. Pot ential unpredictable biological or mechanical compli cations that might occur in an implant supported prostheses make retrievability an important point of consideration and so is the treatment planning. Thus, this case report finds newer means to predict the screw access hole in cases where cement retained prosthesis is indicated.

A technique for the management of screw access opening in cement-retained implant restorations

Introduction: Abutment screw loosening has been considered as a common complication of implant-supported dental prostheses. This problem is more important in cement-retained implant restorations due to their invisible position of the screw access opening. Case Report: This report describes a modified retrievability method for cement-retained implant restorations in the event of abutment screw loosening. The screw access opening was marked with ceramic stain and its porcelain surface was treated using hydrofluoric acid (HF), silane, and adhesive to bond to composite resin. Discussion: The present modified technique facilitates screw access opening and improves the bond between the porcelain and composite resin.

Effect of Metal Extension of Crown in the Screw Access Channel of a Posterior Implant Abutment on the Retention of Cement Retained Prosthesis

Reducing the height of the implant abutment due to limited interarch space decreases the surface area for retention of cemented restorations. The purpose of this in vitro study was to see whether engaging the screw access channel with metal extension compensates for the loss of retention of posterior crowns cemented on shorter abutments. Four identical prefabricated abutments were mounted on implant replicas embedded in acrylic resin blocks. Three of these abutments were reduced in height by 1 mm, 2 mm, and 3 mm respectively and one was left unmodified. Two sets of base metal crowns were fabricated for each abutment, one without and one with the metal extension inside the screw access channel. The crowns were cemented using Tempbond NE. The tensile forces required to separate the cemented crowns from abutments were measured using an Instron testing machine. Statistical analysis of the data was performed using a 2-way analysis of variance and Fisher's protected least significant difference at 0.05 level of significance. An increase of 24% to 261% in retentive forces was observed for the group having metal extension in the screw access channel. Statistically significant differences (P < .001) were found among 2 types of crowns and four heights of abutments. Generally, the retentive forces were reduced in magnitude as the abutment height was reduced. The retention of a casting cemented to posterior implant abutments is influenced by the height of the abutment and the metal extension engaging the screw access channel. The crowns made with a metal extension showed superior retention values.

Occlusal-view photograph of a cement-retained implant prosthesis as a permanent guide for access-hole preparation

Implant-supported fixed restorations can be screw-retained or cement-retained. Pjetursson et al 1 Pjetursson BE Brägger U Lang NP Zwahlen M Comparison of survival and complication rates of tooth-supported fixed dental prostheses (FDPs) and implant-supported FDPs and single crowns (SCs). Clin Oral Implants Res. 2007; 18: 97-113 Crossref PubMed Scopus (560) Google Scholar and Papaspyridakos et al 2 Papaspyridakos P Chen CJ Chuang SK Weber HP Gallucci GO A systematic review of biologic and technical complications with fixed implant rehabilitations for edentulous patients. Int J Oral Maxillofac Implants. 2012; 27: 102-110 PubMed Google Scholar observed that the most frequent technical complications with implant restorations were fracture or chipping of the veneer ceramic, abutment or screw loosening, screw fracture, and loss of retention. These complications necessitate the restorations to be removed, repaired, and reinserted as needed. For removal of cement-retained implant prostheses, it is necessary to access the abutment from the occlusal surface. Locating the site of entry for access-hole preparation to the abutment-screw has been described by several authors. 3 Doerr J Simplified technique for retrieving cemented implant restorations. J Prosthet Dent. 2002; 88: 352-353 Abstract Full Text Full Text PDF PubMed Scopus (41) Google Scholar , 4 Tarlow JL A modified technique to locate the abutment screw access opening of a cemented implant-supported restoration. J Prosthet Dent. 2012; 108: 58-59 Abstract Full Text Full Text PDF PubMed Scopus (17) Google Scholar , 5 Hill EE A simple, permanent index for abutment screw access for cemented implant-supported crowns. J Prosthet Dent. 2007; 97: 313-314 Abstract Full Text Full Text PDF PubMed Scopus (12) Google Scholar , 6 Schwedhelm ER Raigrodski AJ A technique for locating implant abutment screws of posterior cement-retained metal-ceramic restorations with ceramic occlusal surfaces. J Prosthet Dent. 2006; 95: 165-167 Abstract Full Text Full Text PDF PubMed Scopus (45) Google Scholar , 7 Figueras-Alvarez O Cedeño R Cano-Batalla J Cabratosa-Termes J A method for registering the abutment screw position of cement-retained implant restorations. J Prosthet Dent. 2010; 104: 60-62 Abstract Full Text Full Text PDF PubMed Scopus (26) Google Scholar Doerr 3 Doerr J Simplified technique for retrieving cemented implant restorations. J Prosthet Dent. 2002; 88: 352-353 Abstract Full Text Full Text PDF PubMed Scopus (41) Google Scholar and Tarlow 4 Tarlow JL A modified technique to locate the abutment screw access opening of a cemented implant-supported restoration. J Prosthet Dent. 2012; 108: 58-59 Abstract Full Text Full Text PDF PubMed Scopus (17) Google Scholar explained an access-gaining technique by using a vacuum-formed matrix with holes corresponding to abutment positions in which the clinician must preserve the original casts or a vacuum-formed matrix. Hill 5 Hill EE A simple, permanent index for abutment screw access for cemented implant-supported crowns. J Prosthet Dent. 2007; 97: 313-314 Abstract Full Text Full Text PDF PubMed Scopus (12) Google Scholar described preservation of a putty index for the same reason. Schwedhelm and Raigrodski 6 Schwedhelm ER Raigrodski AJ A technique for locating implant abutment screws of posterior cement-retained metal-ceramic restorations with ceramic occlusal surfaces. J Prosthet Dent. 2006; 95: 165-167 Abstract Full Text Full Text PDF PubMed Scopus (45) Google Scholar described a technique which requires placement of a small ceramic stain on the occlusal surface of the restoration during fabrication. Figueras-Alvarez et al 7 Figueras-Alvarez O Cedeño R Cano-Batalla J Cabratosa-Termes J A method for registering the abutment screw position of cement-retained implant restorations. J Prosthet Dent. 2010; 104: 60-62 Abstract Full Text Full Text PDF PubMed Scopus (26) Google Scholar advocated the preservation of a photograph in a computer file as part of the patient's permanent record; however, it involved using complex editing software to superpose 2 digital photographs of the definitive cast with and without the restoration.

Influence of screw access on the retention of cement-retained implant prostheses

Many studies have compared cement-retained and screw-retained implant prostheses. One disadvantage of cement-retained crowns is the lack of predictable retrievability, which can be overcome by creating a screw access channel on the occlusal surface. The purpose of this study was to evaluate the influence of a screw access channel on the retention of cement-retained implant prostheses. Sixteen cast metal crowns were fabricated and divided into 2 groups of 8 specimens each: a control group (CG) comprising 8 cement-retained prostheses and an experimental group (EG) comprising 8 cement-retained prostheses with a screw access channel. Castings were cemented to abutments with RelyX U100, and the opening screw access channels of EG were filled with photopolymerized composite resin (Filtek Supreme XT). The tensile force required to separate the cemented castings from the abutments was measured after 24 hours of cementation with a universal load-testing machine (EMIC DL 2000). A significance level of 5% (α=.05) was considered statistically significant (Statistical analysis was performed by Kolmogorov-Smirnov non-parametric test and the Student t test). The mean force required to achieve the separation was 191 N for the control group (CG) and 161 N for the experimental group (EG). As shown by the nonparametric Kolmogorov-Smirnov test, the dependent variable followed a normal distribution (P=.923). The Student t test found no statistically significant difference (P=.353) between the groups. Fabricating cement-retained implant prostheses with screw access does not compromise or reduce the retention of the crowns.

Simple device for locating the abutment screw position of a cement-retained implant restoration

aAffiliate Faculty, Department of Restorative Dentistry, University of Washington; Private practice, Bellevue, Wash. bProfessor, Department of Restorative Dentistry, University of Washington. (J Prosthet Dent 2013;109:272-274) 1 Plate and guide rod engage abutment screw head on cast, with plate lowered and oriented to buccal of adjacent teeth. Cement-retained implant restorations have been reported to have several advantages over their screwretained counterparts, especially with respect to esthetics, occlusion, cost, passive fit, and reduced chair time.1,2 However, there are occasions when the cement-retained restoration requires removal, for example, if the abutment screws loosen or if the restoration needs repair.3,4 In this instance, the crown frequently remains cemented to the abutment. The abutment screw must then be accessed through the crown. The challenge here is to locate the screw position with minimal damage to the restoration, abutment, and possibly implant. Several authors have reported techniques to achieve this, which include reviewing a radiograph of the implant position and estimating the long axis position of the screw,5 using photography to record the position of the abutment before the crown is cemented,6,7 marking the screw access site with a porcelain stain during fabrication,8 or fabricating a vacuum-formed guide or template over the definitive restoration.9,10 The problems associated with these techniques are clear. Estimating the implant position in 2 dimensions either with radiographic or photographic records is inaccurate.5-7 Marking the screw access point may be useful in nonesthetic areas but has limitations with an anterior restoration.8 This article describes the procedure for fabricating a custom-made and precision implant-locating device (PILD) to record the access position of the abutment screw. It is simple, rapid, inexpensive, and gives 3-dimensional information for guiding directional screw access.

Effects of Abutment and Screw Access Channel Modification on Dislodgement of Cement-Retained Implant-Supported Restorations

This study investigated the influence of implant abutment and screw access channel modification on the retention of copings. Titanium abutment access openings were either left open or modified by placing two vent holes 3 mm from the occlusal edge and 180 degrees apart. Access openings sealed with a resin material were used as controls. Metal copings were cemented and subjected to tensile testing until failure. Access openings with two vent holes resulted in significantly higher mean retention values compared to the opened or sealed screw access groups (P < .05). Cement flow was affected by the internal vent, which increased the area of cementabutment contact.

A three-dimensional image-superimposition CAD/CAM technique to record the position and angulation of the implant abutment screw access channel

Cement-retained, implant-supported restorations have advantages over screw-retained restorations, but retrievability can be a problem. By using computer-aided design and computer-aided manufacturing (CAD/CAM) technology, a working cast or mouth can be scanned, and a definitive record of the screw hole can be made in 3 dimensions and saved as a file. This information includes not only the position of the opening of the screw hole but also its angulation and orientation, which can be retrieved if required.

Factors influencing success of cement versus screw-retained implant restorations: a clinical review

Aim As more and more dental practitioners are focusing on implant-supported fixed restorations, some clinicians favor the use of cement retained restorations while others consider screw retained prosthesis to be the best choice. Discussion In screw-retained restorations, the fastening screw provides a solid joint between the restoration and the implant abutment, while in cement-retained prostheses the restorative screw is eliminated to enhance esthetics, occlusal stability, and passive fit of the restorations. The factors that influence the type of fixation of the prostheses to the implants like passivity of the framework, ease of fabrication, occlusion, esthetics, accessibility, retention and retrievability are discussed in this article with scientific studies demonstrating superior outcomes of one technique over another. Screwretained implant restorations have an advantage of predictable retention, retrievability and lack of potentially retained subgingival cement. However, a few disadvantages exist such as precise placement of the implant for optimal and esthetic location of the screw access hole and obtaining passive fit. On the other hand, cement retained restorations eliminate unesthetic screw access holes, have passive fit of castings, reduced complexity of clinical and lab procedures, enhanced esthetics, reduced cost factors and non disrupted morphology of the occlusal table. Conclusion This article compares the advantages, potential disadvantages and limitations of screw and cement retained restorations and their specific implications in the most common clinical situation.

Three‐Dimensional Location of the Retaining Screw Axis for a Cemented Single Tooth Implant Restoration

Retrievability is a major concern with cemented versus screw-retained implant restorations. This article describes the use of cone beam radiography to help target and create a precise screw access opening for a loosened implant-supported single crown retained by cement to its abutment.

A modified technique to locate the abutment screw access opening of a cemented implant-supported restoration

Cemented implant-supported restorations have advantages relative to those which are screw retained, including greater passivity of fit and better esthetics.1 However, the easier retrievability of a screw-retained restoration is clinically useful should an abutment screw become loose. Abutment loosening of a cemented implant crown usually necessitates estimating the location of the abutment screw access opening, and accessing the screw by drilling through the crown. Several articles have been written describing methods for indicating the location of the abutment screw, either prior to or after the restoration has been cemented.

Effect of axial wall modification on the retention of cement-retained, implant-supported crowns

Compromised angulation of implants may result in abutment preparation that is less than ideal. Compromised abutment preparation may affect the retention of implant-retained crowns. The purpose of this study was to investigate the effect of 5 implant abutment designs on the retention of cement-retained crowns by varying the number and position of the axial walls. Five prefabricated abutments were attached to an implant analog and embedded in an acrylic resin block. The first abutment was left intact without modification. Axial walls were partially removed from the remaining abutments to produce abutments with 3 walls, 2 adjacent walls, 2 opposing walls, and 1 wall. Five crowns were made for each group. The screw access channel for the first abutment was completely filled with composite resin and the rest were partially filled. The retentive surface area of each abutment was calculated. Crowns were cemented with zinc phosphate cement. Tensile force was applied to separate the castings from the abutments. Peak load to dislodgment was recorded. A 1-way ANOVA was used to test for a significant difference followed by the Tukey Honestly Significant Difference test (α=.05). The abutment with 2 opposing axial walls had significantly higher retention than that of all other groups (F=149.9, df =24, P<.001). The abutment with 3 walls exhibited the second highest retention and was significantly greater than abutments with 2 adjacent walls, 1, and 4 walls. Abutments with 2 adjacent walls and 1 wall were not significantly different from each other. The unmodified abutment with 4 walls exhibited the lowest retention despite having a large retentive surface area. The retention of cemented crowns on implant abutments is influenced by the number and position of axial walls.

Design of a surgical instrument for removing bone to provide screw access to a spinal fusion cage

A surgical instrument to aid implantation of a range of lumbar spinal fusion cages has been developed. Once the cage is in position, the entrance to screw holes is partially blocked by the edge of the vertebral body. In order to insert fixation screws to secure the cage between the vertebrae, some part of the blocking edge has to be removed. Rongeurs are currently being used, but they can be time consuming and have the disadvantage that they may remove more bone than is necessary and may cause damage to the fusion cage if not used with care. In addition, access around some of the screw holes may be difficult. The aim of this instrument was to overcome these shortcomings. This paper describes the design of a surgical instrument for cutting edges from vertebral bodies. The development and evaluation of concept designs are presented and discussed. Potential risks were considered and modifications were performed on the selected concept. Functional prototypes were manufactured and tested on sheep lumbar vertebrae. The results showed that the newly designed cutting instrument functions as required and removes the required amount of bone from the vertebral body edge.

Presentation of Two Cases of Immediate Restoration of Implants in the Esthetic Region, Using Facilitate Software and Guides with Stereolithographic Model Surgery Prior to Patient Surgery

Improvements in both implant microsurfaces and placement techniques have reduced healing time and increased survival rates. CAD/CAM technology and improved ceramic materials allow for achievement of improved esthetics at the implant restoration level. Two clinical procedures have the capacity to decrease patient postoperative discomfort and improve esthetics. Flapless surgery reduces surgical trauma and postoperative problems. Placement of the final prosthetic abutment at the time of implant placement stabilizes soft tissue adhesion and position to the implant. Both results require careful presurgical planning with precise implant and abutment placement. This is a clinical report of two cases that are part of a larger ongoing clinical trial of 20 patients. The inclusion criterion was that patients should be missing a single tooth in the esthetic zone. Facilitate™ software was used in conjunction with dicom files transferred from CT scans for diagnosis. Stereolithographic models and surgical guides were fabricated from the digital information. Surgical guides were used preoperatively so implant replicas could be placed in stereolithographic models as simulated surgery. A ZirDesign™ ceramic abutment was adapted on the model, and a provisional crown was fabricated. At the time of actual implant surgery, the same surgical guide was used with a flapless approach. The previously modified ceramic abutment was screw-retained and torqued to place into the implant. The provisional crown was then cemented after blocking out the screw access hole. A final restoration was fabricated from all-ceramic material after several months. Success requires careful patient selection and attention to each step of the technique. Preliminary outcomes from the ongoing clinical trial are promising.

An Esthetic Solution to the Screw-Retained Implant Restoration: Introduction to the Implant Crown Adhesive Plug: Clinical Report

Screw-retained implant crowns may be clinically demanding, especially managing the esthetic and occlusal challenges of screw access channel closure. Many clinicians have moved away from using screw retention as a means of fixing a crown to an implant in favor of cementation to an underlying abutment. A link has been established between peri-implant disease and excess cement extrusion in cement-retained implant restorations. This article describes a novel technique of bonding a pressed porcelain plug into the screw access channel of an implant restoration that allows for control of occlusion, matches the esthetics of a cement-retained crown, and eliminates the issues of excess cement. Overcoming the restorative challenges (esthetic, occlusal) of the screw access channel in a screw-retained implant restoration is difficult. By fabricating a pressed ceramic over metal crown and esthetic plug these challenges can be dealt with in a predictable manner.

Porcelain Fracture Resistance of Screw‐Retained, Cement‐Retained, and Screw‐Cement‐Retained Implant‐Supported Metal Ceramic Posterior Crowns

The purpose of this in vitro study was to compare the porcelain fracture resistance between screw-retained, cement-retained, and combined screw- and cement-retained metal-ceramic (MC) implant-supported posterior single crowns; and to investigate the effect of offsetting the occlusal screw-access opening on porcelain fracture resistance of screw-retained and cement-retained MC implant-supported posterior single crowns. Forty standardized MC molar-shaped restorations were fabricated. The 40 restorations were divided into four groups (SRC, SRO, CRP, and CSC) of 10 specimens each. Group SRC: screw-retained, screw-access hole placed in the center of the occlusal surface; Group SRO: screw-retained, screw access hole placed 1 mm offset from the center of the occlusal surface toward the buccal cusp; Group CRP: cement-retained, zinc phosphate cement was used; Group CSC: cement-retained with a screw-access hole in the center of the occlusal surface. The screw-retained restorations and abutments were directly attached to 3i implant fixtures embedded in acrylic resin blocks. Subsequently, all test specimens were thermocycled and vertically loaded in a universal testing machine at a crosshead speed of 2 mm/min until fracture. Mean values of load at fracture (in N) were calculated in each group and compared with a one-way ANOVA and Tukey's Studentized test (alpha= 0.05). Mean values of loads required to fracture the restorations were as follows (N): Group SRC: 1721 +/- 593; Group SRO: 1885 +/- 491; Group CRP: 3707 +/- 1086; Group CSC: 1700 +/- 526. Groups SRC, SRO, and CSC required a significantly lower force to fracture the porcelain than did the CRP group (p < 0.05). The cement-retained restorations showed significantly higher mean fracture loads than the restorations having screw-access openings in their occlusal surface. The position of the screw-access hole within the occlusal surface did not significantly affect the porcelain fracture resistance.

The use of polytetrafluoroethylene tape for the management of screw access channels in implant-supported prostheses

This article describes a procedure in which polytetrafluoroethylene (PTFE) tape is used to seal the screw access channel to protect the screw head of the abutment and crown screw in implant-supported restorations. The material can be sterilized, is easy to manipulate, radiopaque, and less associated with malodor when retrieved. Malodor is primarily associated with the implant-abutment interface configuration and the suprastructure component design of a given implant system. This technique enables fast removal of the filling material in a single piece, preventing unpredictable and time-consuming manipulations when removal of the screw-retained crown or abutment is required.