Journal of Dental Implants
   About JDI | Search | Ahead of print | Current Issue | Archives | Instructions | SubscribeLogin 
Users Online: 151  Wide layoutNarrow layoutFull screen layout Home Print this page  Email this page Small font size Default font size Increase font size

Table of Contents
Year : 2018  |  Volume : 8  |  Issue : 2  |  Page : 66-68

Cold welding: A possible mechanical complication related to a failing dental implant cover screw

Department of Oral and Maxillofacial Surgery, Albert Szent-Györgyi Medical Center, University of Szeged, Hungary

Date of Web Publication17-Dec-2018

Correspondence Address:
Dr. Veronika Agnes Jancsik
Department of Facial, Oral and Maxillofacial Surgery, Medical School, University of Szeged, 57 Kálvária Street, Szeged
Login to access the Email id

Source of Support: None, Conflict of Interest: None

DOI: 10.4103/jdi.jdi_1_18

Rights and Permissions

Cold welding is a very useful mechanical effect in dental implant therapy when abutments are fixed. However, this effect may cause very challenging situation for the clinicians when occurring in the “wrong place, wrong time.” The incidence of cover screw complications was reported to range 0.5%–8%. According to our investigation, this value may be even higher when conical design present. Although some manufacturers offer so-called retrieval kits, in some cases, these are very time-consuming and not always effective, and when the complication occurs, the planned dental implant therapy could be in danger. This article summarizes a case report when the conical connected cover screw affected from cold welding was removed with a carbide bur.

Keywords: Cover screw, screw-removal techniques, two-stage dental implant surgery

How to cite this article:
Óvári P, Jancsik VA, Piffkó J. Cold welding: A possible mechanical complication related to a failing dental implant cover screw. J Dent Implant 2018;8:66-8

How to cite this URL:
Óvári P, Jancsik VA, Piffkó J. Cold welding: A possible mechanical complication related to a failing dental implant cover screw. J Dent Implant [serial online] 2018 [cited 2019 Sep 22];8:66-8. Available from:

   Introduction Top

Dental implant supported prostheses has been very effective and reliable treatment option since the past three decades. Implants with a conical prosthetic connection are increasingly popular. A successful treatment depends on various biological and mechanical factors, and conical connection facilitates greater stability, smaller microgap, superior preservation of the crestal bone, and soft tissue.[1],[2] However, there are mechanical complications which are barely described in the literature, for example, complications in the conical connected cover screw management. The management of a failed cover screw may play a key role in the dental implant therapy because to initiate the prosthetic phase, the screw has to be removed without damaging the internal threads of the dental implant.[3],[4],[5]

In the background for a failing cover, screw may be several factors, which are summarized in [Table 1] as listed above.
Table 1: The main causes for cover screw failures

Click here to view

These alterations can lead to either a broken cover screw body or a worn-out screw head.[6],[7] The purpose of this article to present an easy method for the removal of a cold-welded cover screw with conical connection.

   Case Report Top

A 64-year-old female patient was referred to the department for oral surgery for the second stage surgery with implant placed in the area tooth number #4. The implant placement procedure (Ankylos, C/X, B11, Dentsply) was carried out 6 months prior her visit, due a maxillary lateral sinus membrane elevation was also conducted during the first stage of the surgery. After the intraoral radiographic verification of osseointegration [Figure 1], the second stage of implant surgery was carried out, with the following techniques described by Bernhart et al.[8] The procedure consisted of the vertical incision on the gingival crest covering the cover screw, and this was followed by a round incision about 1–3 mm around the tissue to be removed. On the platform of the implant, new bone formation was detected, which was gently removed by a 5/6 implant Gracey scaler (Tess Corporation). After this, we attempted to remove the cover screw by manual ratchet applying a reverse torque not >30 Ncm. Several retrievals later, the friction slot of the cover screw became worn out [Figure 2]. Since prior the radiographic examination showed no evidence of the bone growth of the edges, we suggested that maybe cold welding is the cause for the failed manual removal of the cover screw.
Figure 1: Radiographic analysis of osseointegration

Click here to view
Figure 2: Picture of the worn-out friction slot

Click here to view

Cold welding is a very challenging situation due to the high risk of the internal thread damage. After explaining the patient the risk, we decided to remove the cover screw by drilling through the screw with the implant handpiece with a tapered carbide bur (Ankylos retrieval kit, Dentsply). The drilling method included first a clockwise insertion of the bur on low speed on 20 Ncm, for approximately 3-mm deep. This was followed by reverse rotation movement with applying a gentle apical pressure until the cover screw was completely removed [Figure 3]. According to the radiographic examination internal thread if the implant were intact, the abutment fitting was also tested both clinically and by radiograph. After inserting the healing abutment (Ankylos, GH, 4.5 mm), the flap was closed with single knot technique using 5–0 monofilament [Figure 4]. Full contour zirconia prosthesis was delivered to the patient 1 month after the second stage. The result of the 1-year postoperative control is demonstrated in [Figure 5]a, and the radiographic examination result in [Figure 5]b.
Figure 3: The removed cover screw

Click here to view
Figure 4: Wound closure with 5–0 monofilament

Click here to view
Figure 5: (a) One-year postoperative control of the fabricated bilayered zirconia crown. (b) One-year postoperative radiographic control

Click here to view

   Conclusion Top

The above-described case presented a rare complication of cover screw removal the so-called cold welding. Causes for cold welding may be various: nonvisible defect of the cover screw, overtorquing during inserting the screw, but the false direction of unscrewing may also cause cold welding. Unfortunately, in this case, we also could not exclude 100% the presence of bone growth between the implant platform and the internal threads, due to the visible bone growth over the implant platform edges. However, we also could not exclude conical connection as a predisponating factor since it provides a very secure fit but a very tight connection.[9]

While the manual retrieval of cover screw removal failed, analyzing the risk-benefit ratio, and the wish of the patient to save the implant, we decided to apply the drilling through the center of the cover screw method. This method is very easy, safe, cost-effective, applicable on all implant systems but should be concerned if internal bone growth may present due causing damage in the internal threads. Therefore, we suggest this method only in cases where this risk does not occur.

Even for a practicing clinician facing complications in the management of cover screw removal may be very challenging. The problems during the removal may vary from case to case, and so, there is no universal solution for clinical situations with different background. By highlighting several retrieval methods, we hope the case letter may be helpful for all colleagues.

Declaration of patient consent

The authors certify that they have obtained all appropriate patient consent forms. In the form the patient(s) has/have given his/her/their consent for his/her/their images and other clinical information to be reported in the journal. The patients understand that their names and initials will not be published and due efforts will be made to conceal their identity, but anonymity cannot be guaranteed.

Financial support and sponsorship


Conflicts of interest

There are no conflicts of interest.

   References Top

Kaminaka A, Nakano T, Ono S, Kato T, Yatani H. Cone-beam computed tomography evaluation of horizontal and vertical dimensional changes in buccal peri-implant alveolar bone and soft tissue: A 1-year prospective clinical study. Clin Implant Dent Relat Res 2015;17 Suppl 2:e576-85.  Back to cited text no. 1
Moergel M, Rocha S, Messias A, Nicolau P, Guerra F, Wagner W, et al. Radiographic evaluation of conical tapered platform-switched implants in the posterior mandible: 1-year results of a two-center prospective study. Clin Oral Implants Res 2016;27:686-93.  Back to cited text no. 2
Williamson RT, Robinson FG. Retrieval technique for fractured implant screws. J Prosthet Dent 2001;86:549-50.  Back to cited text no. 3
Luterbacher S, Fourmousis I, Lang NP, Brägger U. Fractured prosthetic abutments in osseointegrated implants: A technical complication to cope with. Clin Oral Implants Res 2000;11:163-70.  Back to cited text no. 4
Möllersten L, Lockowandt P, Lindén LA. Comparison of strength and failure mode of seven implant systems: An in vitro test. J Prosthet Dent 1997;78:582-91.  Back to cited text no. 5
Bhuvaneswarri J, Chandrasekaran SC. A technique elucidating the retrieval of an adhered cover screw in a dental implant – A case report. J Clin Diagn Res 2013;7:2642-3.  Back to cited text no. 6
Walia MS, Arora S, Luthra R, Walia PK. Removal of fractured dental implant screw using a new technique: A case report. J Oral Implantol 2012;38:747-50.  Back to cited text no. 7
Bernhart T, Haas R, Mailath G, Watzek G. A minimally invasive second-stage procedure for single-tooth implants. J Prosthet Dent 1998;79:217-9.  Back to cited text no. 8
Goodacre CJ, Kan JY, Rungcharassaeng K. Clinical complications of osseointegrated implants. J Prosthet Dent 1999;81:537-52.  Back to cited text no. 9


  [Figure 1], [Figure 2], [Figure 3], [Figure 4], [Figure 5]

  [Table 1]


    Similar in PUBMED
   Search Pubmed for
   Search in Google Scholar for
 Related articles
    Access Statistics
    Email Alert *
    Add to My List *
* Registration required (free)  

  In this article
   Case Report
    Article Figures
    Article Tables

 Article Access Statistics
    PDF Downloaded0    
    Comments [Add]    

Recommend this journal