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CASE REPORT

Somatoprosthetic Rehabilitation of Digitus Minimus Using Mini-Dental Implant: A Report of Negative Outcome

Aggarwal, Himanshi MDS; Anwar, Mohd MDS; Singh, Saumyendra Vikram MDS; Mishra, Brijesh MS

Author Information
Journal of Prosthetics and Orthotics: January 2020 - Volume 32 - Issue 1 - p 71-75
doi: 10.1097/JPO.0000000000000261
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Abstract

Digitus minimus, the humble fifth finger, is the smallest finger of the hand and is often considered as a bit of a decorative accessory. Conversely, this does not indicate it is insignificant. Together with other fingers, it forms a strong and powerful team. The dynamic function of the little finger is represented by its contributions in grasp, grip, gestures, and absorbing and transferring forces. The little finger contributes to 33% of total hand strength.1 Although the middle and index fingers work with the thumb in grabbing and pinching, the little finger functions with the ring finger to generate hand power.1 Many conditions ranging from congenital disorders to traumatic injury affect the little finger. Alteration in anatomy of the hand is associated with varied emotional and physical responses as well as social restrictions. The responses are associated with aesthetic changes, discomfort, and loss of function.2–6 Microsurgical reconstruction by reimplantation, solitary digit transfer, toe-foot transfer, and use of osteocutaneous flaps have been attempted to reestablish function of some individuals with finger amputation. These procedures may not always be feasible for various reasons3,4,7 As an alternative, prosthodontic rehabilitation with silicone prosthesis is considered.

A major inherent problem with standard silicone digital prostheses is instability. The residuum of the amputated finger should be at least 1.5 cm to fit the standard prosthetic digit.8,9 Inadequate retention may stem from reduced tissue support or weight of prosthesis. A number of methods have been used to augment retention such as medical grade adhesives, adhesive tape, vacuum effect on residual digit, and use of ring at the junction of prosthesis and residual digit.3

For patients with short residual digits, where a conventional prosthesis is not successful, bone-anchored implants may be used as an alternative. Dental implants with a diameter less than or equal to 3 mm (lengths from 10 mm to 18 mm) are called mini-dental implants (MDIs)10 and are often indicated in cases where available bone width is inadequate for conventional implants, but bone quality is not impaired. The single component (one-piece ball end) nonsubmerged mini-implant is categorized as one-stage implant.11,12 Although one-stage surgical procedures using conventional dental implants have been reported,13,14 there are no references for prosthetic rehabilitation of an amputated finger with MDI. The present case report describes use of a mini-implant to retain somatic prosthesis in a patient with traumatic amputation of little finger having insufficient available bone volume to receive a conventional implant.

CASE REPORT

A 23-year-old male patient whose little finger of the left hand was lost at 12 years of age as a result of traumatic injury by a roller machine visited the Department of Prosthodontics for early esthetic rehabilitation, as he was getting married in 2 months. Physical examination revealed the amputation at the level of the proximal interphalangeal joint. Joint mobility and Web spaces were preserved. The residual digit appeared normal, was 1 cm in length, with no signs of infection or inflammation (Figure 1).

F1
Figure 1:
Preoperative view.

After informed written consent was obtained from the patient, implant of retained finger prosthesis was planned. Preoperative cone beam computerized tomographic examination showed inadequate width for conventional implant placement. An MDI (Equinox, Myriad plus implant system, the Netherlands), 11 mm in length and 2.5 mm in diameter, was selected. By its aggressive thread design, self-tapping, and bone condensing feature, this MDI is intended to be placed via a one-stage surgical procedure.12

Under regional anesthesia (brachial block) and an ischemic tourniquet control, an ellipsoid flap was raised with debulking of skin flap to prevent “wobble” of the implant later.14

Implant osteotomy was completed with a single 1.5-mm pilot drill. Drill depth was restricted to one half the implant length so as to cause bone condensation during mini-implant insertion.12 Implant insertion was done into prepared osteotomy with insertion torque above 35 Ncm. Initial implant stability was recorded as 68 ISQ by resonance frequency analysis (RFA). Flaps were sutured with 3–0 silk (Figure 2). Postoperative radiograph was taken to confirm the accuracy of implant placement. Analgesics and antibiotics were prescribed,5 and postoperative instructions were given. The wound was inspected after 7 days and sutures removed.

F2
Figure 2:
Immediate postoperative view.

In the fourth week of follow-up, implant stability was 74 ISQ by RFA. Prosthetic rehabilitation was initiated with attachment of transfer coping to the ball attachment. Pickup impression was taken with polyvinyl siloxane elastomeric impression material (Aquasil, Dentsply, United Kingdom). Implant analogue was attached to transfer coping after pickup impression. Impression was poured with type IV dental stone (Kalstone, Kalabhai Pvt. Ltd, Mumbai, India). Once the impression material had set, a working model was recovered and transfer coping was removed from implant analogue. Female metal housing was then attached with ball attachment on the residual digit model (Figure 3). To facilitate bonding between silicone and metallic attachment, metal housing was covered in an autopolymerizing acrylic resin cap (Pyrex polymers, Roorkee, India; Figure 4).

F3
Figure 3:
Residual digit model with female metal housing.
F4
Figure 4:
Acrylic resin cap over female housing.

Impression of the little finger of the other hand was made with an irreversible hydrocolloid impression material (Zelgan; Dental Products of India, Mumbai, India); molten modeling wax was poured into the negative mold of the finger. At the same time, the residual digit model (lubricated) with resin-covered female housing was placed into the corresponding finger space of alginate impression. Wax pattern along with residual digit was recovered, and necessary modifications were made to simulate the left little finger. After satisfactory try-in of wax pattern (Figure 5), the residual digit model along with wax pattern was invested to obtain a two-piece mold. After dewaxing, separate shade matching was done for dorsal and ventral aspect of the finger by using digital spectrophotometer (E-spectrophotometer; Factor-II Inc. SPECTRO). Silicone material (M511; Technovent, United Kingdom) was layered into the mold in required locations; primer (Platinum primer-G611; Technovent, United Kingdom) was applied to the acrylic cap of female housing. The packed silicone material was cured at 100°C for 1 hour. After sufficient cooling, the prosthesis was carefully retrieved and finished. Fit and retention of prosthesis was evaluated. Extrinsic stains were applied in natural daylight for final shade matching. Prosthesis was delivered to the patient (Figure 6). Instructions for care were given. The patient was advised against applying heavy pressure on the finger or excessive sun/dust/dirt exposure. The appearance of the prosthesis was scored subjectively using a visual analogue scale (VAS)15 as excellent (score, 8). Although the patient was not very concerned about function with the prosthetic finger, it was assessed objectively by using the Jebsen Hand Function Test, which evaluates hand function by the time taken to carry out specific daily activities.16 The test displayed consistently slower functions with prosthesis fitted hand compared with the contralateral normal hand. The patient was also able to perform some activities such as grasping and holding light objects. Patient was recalled initially 1 week after prosthesis insertion and further after 1 month for periodic evaluation.

F5
Figure 5:
Wax pattern try-in.
F6
Figure 6:
Final prosthesis.

The follow-up of the patient at 2 months, however, revealed some biological complications related to peri-implantitis, pain, soft tissue swelling, and implant mobility. Efforts were made to prevent implant failure by oral antibiotics, rest, and hygiene procedures, but unfortunately, the implant failed at 3-month follow-up. The implant was removed and space was created and filled with graft material to preserve bone for future implant placement.

DISCUSSION

Total or partial amputations of digit leave individuals with an inevitable abnormality and variable function of the hand. Although vacuum-retained prostheses can provide exceptional aesthetics for some amputations, they require sufficient residual finger length and are prone to dislodgement. These shortcomings of conventional prostheses might be mitigated by using bone-anchored implants.2,5,8,9

Apart from providing a secure attachment for a prosthesis, a titanium implant offers additional advantages such as less feeling of weight, more control over the prosthesis, and possible restoration of some tactile feedback.14,17 The vibration and position sensations acquired by osseointegration of the implant have been described as “osseoperception” by Lundborg et al.5 The phenomenon is based on transmission of tactile stimuli from bone to intraosseous nerves through the osseointegrated implant. Aydin et al.2 and Doppen et al.8 have described the use of bone-integrated conventional oral implants with customized attachments to retain finger prostheses. In the present case, MDI with O-ring system for retention was used. This resilient retention system is composed of a metal housing and a rubber ring. The hexagon-shaped base of the retention unit provides an antirotational feature.

The surgical and prosthetic protocols followed in the present case for placement of MDI in amputated digit were adapted from intraoral mini-implant protocol.11,12 The majority of authors have advocated conventional (two-stage) surgical procedure for implant placement mainly for two reasons: to prevent infection and to prevent early implant failure owing to loading with prosthesis.7 Number of stages also depends on the initial/primary stability of the inserted implant and quality of bone at the implant site. The self-tapping design of MDI led to bone compression and condensation during its insertion, which ultimately helps to establish good primary stability. Therefore, early loading was carried out with prosthesis. Amornvit et al.13 and Yeshwante et al.17 have also reported one-stage technique for implant (conventional) placement to retain finger prosthesis.

Less treatment time, less postoperative pain, fewer hospital visits, ability of immediate loading after surgery, and cost-effectiveness are some of the advantages of MDI compared with two-stage surgery using conventional implants.10 The smaller diameter of MDIs allows them to be successful in cases with limited bone that might not be a candidate for conventional wide-diameter implants. MDI are less invasive and can be placed and loaded on same day, or some days after implant placement as compared with their wider counterparts.

The outcomes of the present case showed that an implant-retained finger prosthesis provides a high level of aesthetic enhancement and limited functional enhancement as well. Successful osseointegration and excellent prognoses have been reported for various titanium implants used in finger rehabilitation2,5,9,13; however, failures do exist in literature.8,14 Doppen et al.8 reported implant failure owing to infection, and Sierakowski et al.14 addressed loosening of implant due to trauma. In the present report, an implant was placed in the little finger, which failed at 3-month follow-up. Failure might be attributed to the following: inappropriate selection of case, early loading of implants, excessive functioning with prosthesis, and inability to maintain adequate soft tissue hygiene.

Once an implant has been removed for any reason, it is feasible, after allowing soft and hard tissue to resolve, to repeat the entire process, provided healing is uneventful.

The take-home lessons from this case included need for a shorter follow-up timeline with early implant loading, better case selection, and great emphasis on initial and long-term follow-up instructions. With MDI, there is guarded prognosis with early loading protocol in case of MDI-retained finger prosthesis; therefore, one may prefer delivering an MDI-retained finger prosthesis at least 4 to 6 months postimplant placement.

CONCLUSIONS

The use of osseointegrated MDIs to retain finger prostheses in patients with short residual fingers seems to be a viable clinical concept as it provides aesthetics, function, and generally excellent retention to the prostheses, although some complications and failure might be experienced. One-stage surgery reduces the treatment time and could provide more comfort and psychological satisfaction to the patient. However, this approach should be used cautiously as it is technique sensitive, requires an expert multidisciplinary team, careful patient selection, and suitable follow-up of surgical and prosthetic protocols as well as proper home care and hygiene. Long-term studies of implant-retained finger prostheses are needed.

REFERENCES

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Keywords:

mini-dental implants; digitus minimus; somatoprosthesis

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