Authors: DR. B.S.SALUJA, DR. DIVYA MITTAL

GURU NANAK DEV DENTAL COLLEGE AND RESEARCH INSTITUTE, SUNAM.

ABSTRACT
During the last two decades, implant treatment has become one of the first options for the prosthetic rehabilitation of completely edentulous and partially edentulous jaws. Slow and steady shift of paradigm from conventional two pieces, two stage implantology to unibody single stage implantology is already on the horizon. The unibody design mimics natural tooth with seamless transition of radicular unit to coronal unit. The one piece implant reduces the requirement of multiple surgical and prosthetic components, thereby reducing the inventory and cost. It also eliminates structural weakness built into two piece implant system.

INTRODUCTION
With osseointegration now being established scientific phenomena the major thrust in implantology is directed towards improving the design of implants, simplifying the surgical protocol, immediate placement and loading of the implants, and to reduce the restoration time. The conventional two piece implant design feature has the implant -abutment connection, rendering the design with a weak link in the entire assembly. A seamless transition from the root analogue to the crown analogue overcomes this disadvantage of the two piece (split) implant^2,12. The implant is made with the bone anchoring portion, the soft mucosa-traversing portion, and the prosthetic abutment as 1 piece9. One Piece implant actually mimics the natural tooth in its construction.^2,12.

CONCEPTS FOR THE EVOLUTION OF ONE PIECE IMPLANT
The concepts which lead to evolution of one piece implant are:

1. SIMPLIFICATION OF BRANEMARK CONCEPT:
Legendary scientist PI Branemark introduced two piece implant with two stage surgical procedure1. During the first surgical procedure, it was necessary that the end osseous root analogue be allowed to heal, submerged and unloaded for the period of 3 to 6 months in the bone on the basis of the prevailing understanding of osseointegration and designing of the implants³. 2nd stage surgery was required to expose the submerged implant to proceed with a restorative phase where again a short healing phase for the soft tissue was required to form a well healed collar of tissue around the neck of the implant. The crown analogue abutment was attached through a screw to the internal body of implant⁷.
But now with the improvement in the designing of implant, better understanding of the factors affecting osseointegration, it is possible to achieve and maintain osseointegration with one piece implant also.⁷


2. IMMEDIATE LOADING OF IMPLANTS:
   
   • Good primary stability of implant is there. About 35-45Ncm torque is required for the primary stability of implants.^4,9,11
   • Controlled occlusal loading should be done as heavy occlusal loading will lead to implant failure.^5,10
Implants can be placed in a single stage and loaded immediately with provisional restoration if


3. IMMEDIATE PLACEMENT OF IMPLANTS:
   Immediate placement of implant means that the crown is given the very next day of the implant placement. It is especially applicable in cases of fresh extraction sockets. In this case, two piece implant has no scope as there is no flap closure and abutment has to be joined to the root implant in the same appointment. But in case of one piece implant, socket guides the portion of implant and the emergence of abutment matches the natural tooth which gives better esthetics to the restoration. It also leads to the preservation of the alveolar bone height and width and preservation of soft tissue which lead to better esthetics^5,6,8

ONE PIECE IMPLANT VS TWO PIECE IMPLANT
One piece implant and two piece implants will be discussed on the further following features:

1. MARGINAL BONE LOSS:
One piece implant has no micro gap between implant and the abutment, thus, the loss of alveolar bone around the implant is minimized as it can’t harbor bacteria. But in two piece implant as this micro gap is present, thus, micro leakage and micro movement of prosthetic abutment can occur and local inflammation of soft tissue around implant may develop. Stable marginal bone levels around implant supports its clinical use¹⁰.
One piece implant enables the undisturbed healing of peri-implant soft tissue and avoids disruption of soft tissue seal when placing definitive prosthetic restoration.Also, width of one piece implant is similar to biological width of natural teeth and gingival margin may be placed more coronal than when two piece implants are used.
Marginal bone loss is generally calculated with following formula¹⁰:



Marginal bone loss= Radiographic bone loss × known implant length Radiographic implant length

REFERENCE POINT FOR THE RADIOGRAPHIC EVALUTION


The marginal bone level, that is, the position of the marginal bone as compared to a reference point on the implant, was evaluated. The reference point used for the readings was the lower corner of the implant collar.⁹In a study done by Siepenkothen⁹ in 2007, the bone level was readable for 82% of the implants after 12 months or more, a percentage normally encountered in clinical radiographic analyses. In another study done by Finne4 et al in2007 the mean (SD) change in bone level between years 1 and 2 was 0.08 mm (1.19) (95% CI–0.30 to 0.46) (P=.68), demonstrating a stable marginal bone level. Normal implant mucosa was noted for approximately 90% of the sites at the 1-year follow-up.


2. MECHANICAL STRENGTH:
With the elimination of abutment screw, there is no empty space in the implant which provides sufficient strength to one piece implant despite of its smaller diameter as compared to two piece implant^6,10. In one piece implant, implant cross-section is solid as compared to hollow cross-sectional area for two piece implant⁹.Implant with 2mm diameter has fracture strength 16 times lower than 4mm diameter implant as reduction in 1mm diameter of implant, reduces the contact area by 40%. Thus


3. PROSTHETIC PHASE:
Conventional two piece implants require a healing abutment around which soft tissue have to heal after 2nd stage surgery and they require separate different prosthetic components, impression coping each different for closed tray or open tray impression techniques and also implant analogue for lab models.
One piece implant which comes with an in built abutment. One piece implant has friction fit healing abutment. The abutments are prepared with proprietary TC burs following the principles of FPD preparations with which all are familiar and comfortable. Impression procedure are identical to the crown and bridge work, require gingival retraction and impression making with suitable impression techniques of putty wash or custom tray regular body method. Presence of friction fit abutment eliminates the cement or acrylic resin forced below the soft tissue margin of provisional restoration and contact of acrylic resin and monomer with raw wound edges.¹¹ Laboratory phase of making restoration is also easy, and simple similar to that of the conventional FPD technique with which many dental commercial laboratories are familiar with. The cementation procedure with one piece implant is completed and checked with IOPA radiograph to confirm complete removal of set cement⁷.


4. IMPLANT SURVIVAL RATE:
Implant survival was based on the fact that each implant performed its purported function, that individual implants or fixed partial dentures were stable, as evaluated manually by using the back ends of 2 instruments on each side of the prosthesis or implant to determine if movement was present, that no pain or infection was observed, and that the radiographs were without indications of pathologic bone loss9.The cumulative survival rate in one piece implant is about 98-100% as shown by various studies^4,5,6,9,10.
In a study done by Finne4 et al in 2007,the 1-year results from this multicenter study evaluating the daily use of the 1-piece implant treatment concept demonstrated an implant survival rate of 98.7%.In another study done by Siepenkothen⁹ in 2007 showed CSR of 100%. The data from this study supported the fact that it is possible to achieve similar clinical results using a 1-piece implant system instead of a 2-piece implant system with a simpler and more patient-pleasing clinical protocol. In another study done by Hahn⁶ in 2007,forty-seven implants were placed in 30 subjects demonstrated the beneficial marginal bone levels and a survival rate of 97.9% after up to 3 years of loading.

SURGICAL PROTOCOL OF USING ONE PIECE IMPLANT
Since the 1stage non submerged technique did not require flap closure over the implants inserted into the bone a flapless approach was evolved to place implants thereby eliminating the need of rising a flap, sutures, decreased blood loss and less post operative pain, reduced the appointments and cost of surgical procedures and also have good tissue response⁴. Response of the soft tissue around implants with flapless surgical technique is predictable. The soft tissues demonstrate less of inflation and probing depth around implants. The crestal bone changes around implants are also minimal. The other advantages of flapless surgical procedure over flap procedure are^5,9:

• Decreased post-operative discomfort and swelling as there is decreased likelihood of manipulation of tissues.
• As there is no need to raise the flap, thus, there is minimal bleeding at the surgical site and no need of stitches.
• Both the surgical and the healing time are also decreased.
• Blood supply to the surgical site is maintained, thus, there is decreased likelihood of bone resorption. The esthetic results are much more obvious than two piece implant
• One piece implant also demonstrates biological width similar to natural tooth

INDICATIONS FOR ONE PIECE IMPLANT

1. NARROW EDENTULOUS SPACES:
One piece implants are generally indicated in sites with narrow labiolingual width and limited interdental space. The two piece implants in these sites face mechanical challenge as diameter of implant body has to be decreased and it becomes structurally weak to accommodate the screw. Also , it is difficult to achieve good esthetic results with large diameter implants. To prevent the interproximal bone resorption and loss of gingival papilla volume in esthetic zone, a space of atleast 1.5mm is necessary between implant and each adjacent tooth. Now, when the labiolingual dimensions are decreased and amount of bone available is 4mm wide then, placement of standard width implant leads to exposure of implant threads. Thus, the use of small diameter implants lead to restoration without bone grafting.^10.
2. Immediate placement in fresh extraction socket:
it is generally indicated in fresh extraction socket sites as socket guides the portion of implant and emergence of abutment matches the natural tooth^5,8.

LIMITATIONS OF ONE PIECE IMPLANT:

1. In posterior edentulous areas as heavy occlusal loads are applied over the restoration immediately^5,10.
2. It can’t be used in case of tilted abutments9( tilt not more than 10-15°)
3. It allows only the use of knife edge margin for the final prosthesis as providing chamfer of shoulder to final restoration leads to structural weakness in the final restoration¹⁰.

CONCLUSION:
The field of implantology is constantly evolving and new paradigms created by the attempt of man to copy nature in implantology reflects the most, in OPI which has a similar seamless transition from radicular part to coronal part, with passage of time and new evidence emerging to reinforce the success of OPI.THUS, ONE PIECE IMPLANT OFFERS ATTRACTIVE AND EASY ALTERNATIVE TO TWO PIECE IMPLANT FOR EASY TREATMENT WITH IMMEDIATE PROVISIONAL RESTORATION.

REFERENCES:

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