Retrieval of Fractured Screws from Dental
Implants – A Case Report
Nischal K1* and Chowdhary R2
1Researcher, Department of Prosthodontics, Rajarajeswari Dental College and Hospital, India
2Professor, Department of Prosthodontics, Rajarajeswari Dental College and Hospital, India
Submission: November 15, 2017; Published: April 26, 2018
*Corresponding author: Kunal Nischal, Department of Prosthodontics, Rajarajeswari dental college and hospital, Bengaluru-560074, India,
Email: [email protected]
How to cite this article:Nischal K, Chowdhary R. Retrieval of Fractured Screws from Dental Implants – A Case Report. A Preliminary Study. Adv Dent & Oral
Health. 2018; 8(4): 555741. DOI: 10.19080/ADOH.2018.08.555741
Introduction of dental implant to prosthetic dentistry has provided an alternative to rehabilitate edentulous patients. Rehabilitation with implants is nowadays considered a predictable solution, with increased success rates. However, biological and technical complications are frequent.
Implant therapy is a very effective and reliable method involved in the treatment of complete or partial edentulism . The success of dental implant treatment depends on biological and mechanical factors. Biologically the success of dental implant depends on the long term osseointegration which is sensitive to atraumatic implant placement and restoration . This type of prosthesis significantly improves the quality of life of the edentulous patients as compared to conventional compete denture patients, since they offer functional, aesthetical and psychological advantages . Nevertheless a series of mechanical complications had been registered with the employment of this type of prosthesis .
Sekine et al.  in a study found that a mobility range of 17 to 58 microns labially and 17 to 66 microns lingually for osseointegrated implants with load of upto 2000g, results in bone deformation. This is in contrast to 100 and 200 microns range associated with periodontal ligament . Because of less movement of the implant the precision of cast framework would be more crucial with fixed prosthesis when connected to dental implants . Mechanically the success depends on the implant, its components (transmucosal abutment and abutment screw), prosthesis (prosthetic screw). One of the most common mechanical complications include screw loosening (abutment or prosthetic), screw fracture and problems with overdenture attachments .
Implant abutment connections plays a significant role in complication of screw loosening. An implant having a short (< 2mm) external hex at the prospective connection with the abutment seems to be especially prone to screw loosening as
compared to internal taper/conical implant abutment connection with anti-rotational feature . A high incidence of screw loosening of upto 40% was found for external hex connection as reported by Becker W and Becker BE . In contrast, Levine et al reported lower rate of abutment screw loosening of about 3.6%-5.3% with conical implant-abutment connections, restoring single-tooth replacements with cemented crowns [10,11].
A 65 years old lady reported, with a chief complaint of loose upper and lower hybrid dentures. Earlier history revealed that, she was treated one year back with All-on-four concept of implants in both maxillary and mandibular edentulous arch for hybrid prosthesis. After around 7 months of restoration, patient
came back to the department, with loosening of the maxillary and
mandibular prosthesis. Clinical and radio-graphical examination
revealed fractured prosthetic screw in three multiunit abutments,
in region of 22, 32, 42 and the frameworks were not passively
seated (Figure 1-3). After explaining the situation to the patient,
it was decided to remove the broken screws and replaced with
newer prosthetic screws with complete new hybrid prosthesis as
the casted frameworks were not passive.
a) The multiunit abutments with broken screws were
retrieved from the implants by engaging the external hex of
the straight multiunit abutment
b) Under magnifying glass with a needle diamond bur (No.
101, Shofu INC, Kyoto, Japan) of air rotor (NSK, Ti-Max Z900
L, Tokyo, Japan) without water spray for proper visibility a
fissure was created on the head of the broken screws.
c) A modified spoon excavator (ESC 820, GDC, INDIA)
was used as a screw driver, which was engaged in the fissure
created and rotated anti- clockwise to remove the broken
screws (Figure 4-6).
d) New both maxillary and mandibular hybrid prosthesis
were then fabricated as the frameworks were not passive
(Figure 7). Post prosthesis oral pantomograph showed a
passively seated hybrid prosthesis framework (Figure 8).
e) Patient was followed up for 2 years, every 6 months. No
further complication occurred during the follow up period.
The desirability of “passive fit” of implant prosthesis is
generally recognised, as it is considered as the “holy grail of
the discerning implant prosthodontists” [12,13]. The concept
of passive fit remains controversial and has been understood
partially . Although failure to eliminate distortion between the
frameworks and implant abutments has been one of the reason
for biologic complication or delayed component failure .
Therefore misfit in case of implant supported prosthesis will be
more destructive and this misfit can lead to serious screw joint
complications. Screw-joint involves a number of critical factors
such as, adequate preload, precision fit of implant components
and basis antirotational characteristics of implant to abutment
connection . Torqueing of an abutment has a clamping effect,
called the preload which causes elongation of the screw . The
clamping force is directly proportional to the force used to tighten
the screw. The suggested amount of the torque for a preload should
be 75% of the value to reach permanent deformation to provide a
safety value for the screw joint . The most common causes of
screw loosening and fracture have been categorised as inadequate
tightening, adverse occlusal forces and fatigue character and
yielding strength of the screw material [19,20]. Moreover, the
surface of new metal screw has surface imperfections in the form
of high spots, grooves and irregularities, such that when initial
load is applied only the high spots on the screw will be in contact.
Flattening and wear of these high spots is described as settling of
screw and which results in loss of some initial preload . Binon
 suggested that a mean flat to flat range of less than 0.005 mm
on the same hexagon and a flat to flat range of less than 0.05 mm
for the entire sample results in a more stable screw joint . The
relationship between torque and preload is not linear . Friction
should also be considered in the system. Approximately 90%of the
applied torque is lost as friction. Depending on manufacturer and
system recommended torque values range between 20 to 35 Ncm
and a torque wrench is required to obtain a more consistent value
. However a screw is tightened until plastic deformation takes
place and loss of preload occurs with possibility of screw loosening
and fracture. The stability of implant abutment connection is
influenced by factors such as internal /external connection,
screw head design, screw geometry, materials, screw diameter
and overall screw mechanics. Relative to external hexagon
internal implant abutment connection shows higher stability and
improved force distribution . To maximise the preload and
minimize the loss of input torque to friction, the head of the screw
should be wider than the thread diameter of the screw . The
head most often should be flat to dissipate stresses more evenly
within the threads and head of the screw . These screws
are of either gold or titanium or gold-coated titanium with the
tensile and yield strengths being highest for gold screws [27,28].
The major disadvantage of titanium screws is their tendency to
cause galling, which results in excessive friction between the two
mating surfaces thereby causing localised welding with a further
roughening of mating surfaces . Galling occurs in the following
manner. Ttanium of the retaining screws slide in contact with the
titanium of the implant body, the coefficient of friction increases
whereby titanium molecules transfer from the mating surfaces
. This has been described as adhesive wear mechanism which
causes damage to both implant and screw threads . Screw
fracture and loosening are closely linked. It has been suggested
that screw loosening is the initial stage of screw fracture .
When a screw loosens damage occurs at high stress locations
like screw heads and first thread. Consequently loose abutment
screw should always be replaced as a loose screw could have a
fatigue history predisposing it to fracture . Williams in a study
reported that hydrogen at concentrations as low as 200 ppm (by
mass) can cause marked reduction in ductility of titanium and
plastic deformation of the screw can accelerate absorption of
hydrogen which makes screws vulnerable to fracture [33,34].
This case demonstrates the need to consider all possibilities
when faced with abutment screw loosening or fracture and further
highlights the need for multidisciplinary skills in the treatment of
patients with implants.