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IMPLANT DENTISTRY - Unilateral SUBPERIOSTEAL Implant.

Dr. Haseeb Dary*

*dary_haseeb@yahoo.com

Keywords: Unilateral subperiosteal implant - Insufficient bone - Bone impression

When the volume of the residual alveolar ridge is insufficient to receive endosteal implants, use of the unilateral subperiosteal implant is one of the treatments of choice.1, 2

This modality of implants has comparable success and survival rates.1, 3, 4 It was specifically developed to treat patients with insufficient available bone in the alveolar ridge; it shouldn't be used for patients with overabundant bone.1

The surgical protocol in the case presented is comprised of a two-stage surgery, the first of which results in taking a direct bone impression and the second in placing the custom-made implant. The subperiosteal implant is designed to rest on the surface of bone, under the periosteum rather than gaining endosteal support as teeth or most alloplastic implants used in the body, this implant distributes stresses from the prosthesis to large areas of bone in a manner similar to a snowshoe.5

A customized casting made of surgical metal adheres to the bone with a combination of fibrous tissue and direct bone support2, NO OSSEO INTEGRATION. Permucosal abutment posts and intraoral bars are designed for prosthesis retention.5

So subperiosteal implants are used when there is an insufficient available bone which differs by volume from case to case. That's why it was classified into four divisions. In our case there is a deficiency in the height of bone which classify the case under the division C-h available bone

This division of available bone maybe treated by a number of different implant approaches. The most common is root form implants of reduced height. The second option is augmentation.

Or the third option is the subperiosteal implant5, which is going to be presented in this article.

DIVISIONS OF AVAILABLE BONE According to misch(5)

DIVISION

A (Abundant Bone)

Division A forms soon after the tooth is extracted. Division A corresponds to abundant available bone in all dimensions

DIMENSION:

>5 mm width

>10 -13 mm height

>7 mm length

12 mm length

or = 1

DIVISION

D (Deficient Bone)

Long term bone resorption may result in this complete loss of the alveolar process accompanied with basal bone atrophy.

Sever atrophy describes the clinical condition of the Division D ridge.

DIMENSION:

Severe atrophy

Basal Bone

Flat maxilla

Pencil thin mandible

Terminology

The terminology for the subperiosteal implant includes portions of the implant below and above the soft tissue.5 The substructure is the portion of the implant that is responsible for the support of the implant and is located below the periosteum, on top of the bone. It consists of several struts:

Primary struts are the major components of the substructure and can be either peripheral or abutment. The peripheral struts are the outermost regions of the implant and lay on the most extended areas of the cortical bone.

The abutment struts connect the labial and lingual peripheral struts and a vertical permucosal post on the crest of the edentulous ridge. Secondary struts help dissipate the forces from the primary abutment struts, improve the rigidity and casting of the substructure, and serve as an additional support mechanism of the implant. (Not used in this case)

The permucosal abutment posts exit through the mucosa, and act as prosthetic retainers. The uperstructure connects the abutment posts designed above the soft tissue. This structure both retains and supports the pros- thesis during function and distributes occlusal loads to the sub- structure below the soft tissue.

Mode of tissue integration

Subperiosteal implants heal in the periosteal mode of tissue integration. They are enveloped in a dense fibrous collagenous tissue sheath constituting the outer layer of the periosteum. Functional forces are absorbed by the underlying bone through the periosteum.1, 6, 7

Case report

A 60 years old healthy female came into the clinic asking for a fixed dental appliance to restore the bilateral edentulous posterior spaces of her own (Kennedy class 1).

There was a missing 6 and 7 on each side with compromised 4 and 5 on each.

The volume of available bone was insufficient to place a root form implant on the site of 7 (C-h available bone) a ridge mapping technique was used and a (C-w available bone) was also encountered.

The use of short implant in this case was not a treatment of choice; the crown - implant ratio is > 1. A unilateral subperiosteal implant was suggested.

Surgery

A two stage surgical appointment is usually suggested, (Berman introduced the Two-surgery technique in the 1950s8) separated by at least 6 weeks.5

First surgery

Infiltration was administered with long acting anesthetic (UbistesinTM forte 4%) to anesthetize the residual ridge posteri- or to the mental foramina from buccal and lingual sides and the lateral aspect of the ascending ramus.

An intraoral and extra oral scrub of the patient is performed with Chlorhexidine.5

Soft tissue reflection

Incision

The incision begins at the retro molar papilla at the base of the retro molar pad to the premolar. A full thickness incision through the periosteum scores the underlying bone.

Reflections

A full thickness periosteal reflection exposes the underlying residual ridge and lateral regions of the mandible.

Evaluation of the crest

A knife edge ridge was exposed, thin knife like edges resorb shortly after implant insertion, if not before.5 An osteoplasty was performed to recontour the bone so the crest is broad enough to have a blood supply from the underlying trabecular bone. The osteoplasty was performed at the bone impression appointment. In this way the several weeks interval permit initial remodeling.

Impression

Types of Impression Materials

Three major types of elastic materials are used in implant dentistry for obtaining the direct bone impression: polysulfides, silicones, and polyethers. The material which was used in this case is addition silicone (GhenesylTM silicone first impression: putty soft. low viscosity).

Making the Impression

A retraction sutures (3-0 atraumatic black silk sutures1) are made to attach the reflected tissues to the mucosa of the cheek - from buccal side - and the lingual side reflected tissues are anchored on the teeth of the contra lateral side, this technique would open a space to take the impression.The gloves are moistened to prevent the impression material from sticking. A small rolled por- tion of putty was placed into the tunnel of the reflection and molded along the exposed underlying residual ridge no trays are needed in this technique.

After complete setting the impression is gently lifted. Saline irrigations used to rinse and moisten the tissue, and all reflected regions are inspected for remnants of impression material. The direct bone impression is evaluated for all necessary land marks. The retraction sutures were removed and the tissue re-approximated and sutured. The contra lateral side was treated in a similar fashion.

Implant Fabrication

The subperiosteal implant is fabricated-casted with pure titanium. Laboratories should be members of ASTM (American Society for Testing and Materials) and should not determine their own procedures and techniques.9

The implant design in this case composed of one abutment con- nected to the peripheral struts by 4 abutment struts for each implant. One hole was drilled on each implant on a peripheral strut (distal aspect) for the placement of titanium fixation screw. Implants should be thoroughly cleaned and sterilized before placement.

Implant insertion (second surgery):

The surgical insertion of the implant is very similar to the direct bone impression surgery but is more rapid and causes less swelling and discomfort to the patient. After the implant is placed on the ridge a titanium screw is used to fix the implant on the ridge to obtain the primary stability this screw would be of no use after the healing of tissues because the implant would be stable on place by the attachment of the soft tissues to the bone which holds the struts of the implant in between.

The site is then sutured again.

Sutures were removed after 1 week.

Prosthesis

After 2 weeks of implant placement the patient came back. A preparation was done to the premolars at both sides and the impression was taken.

4 units bridge was fabricated for each side splinting the implant abutment to the 2 natural teeth of each side.

Cementation

(DentoTemp of ITENA) long term temporary cement which is used as a Permanent cementation of implant-retained crowns.

Discussion

In summary, the advantages of subperiosteal implants include: The predictability of the results and the high success rate, the survival and success rates of modern-day subperiosteal implants are equal to or greater than root form implants when placed into C-h bone.5

Noninvasive surgeries are preferred compared to the use of iliac crest bone grafts10, the trauma would be in one site (which is the oral cavity) not in 2 sites. When using the iliac graft the patient would go with pain while he walks out of the operation in addi- tion to the pain in his mouth.

No possibility of parasthesia. This may be the case when nerve repositioning is performed to enhance the bone height to place the root form implants in the mandible. No bone grafts needed with any possibility of bone graft failure which requires re-grafting of the area with all accompanying trauma and time consumption.

Less expensive procedure when comparing restoring one segment or one side of the arch with bone grafting or sinus lifts and sev- eral root form implants to a one subperiosteal implant with 1 or more abutment, the expenses would be way less than the bone grafting procedures.

Time preserving

Disadvantages include the initial complexity of the surgical pro- cedures. This complexity presumes a certain level of experience that the practitioner can obtain only over a long period of time. The procedures require specialized technicians and a titanium melting oven.

After 3 years Also the disadvantages include the frequent necessity for 2 surgical procedures, this can be overcome by the use of (CAD-CAM)11 but again it's not considered a mainstream procedure because of technique sensitivity and cost.

Finally, removal of subperiosteal implants, although rarely indi- cated, can present difficulties.

In a case report under the title REPLACEMENT OF A MANDIBULAR SUBPERIOSTEAL IMPLANT12 the author replaced a subperiosteal implant, which had been in successful service for approximately 15 years. Both the implant and prosthesis had been in service. Although the patient had been given the option of an augmentation using an autogenous iliac crest graft with subsequent insertion of endosteal implants. The importance and potential benefits of subperiosteal implants are undeniable, being at this time the only means of restoring jaws in situations where endosseous implants cannot be placed.

Subperiosteal implants often serve our most troubled patients. For patients who exhibit severe mandibular and maxillary alveolar ridge atrophy, no other treatment options may exist.13

Conclusion

Alveolar ridges with severe atrophy can be reconstructed pros- thetically (fixed and removable) with less time compared to bone grafting procedures. Partial subperiosteal implants can be used with endosseous implants and even natural teeth with fixed bridges. The surgical technique and clinical stages are not complicated, generally being mastered by implantologists in general dental practice.

REFERENCES

1 Principles and practice of implant dentistry Charles M. Weiss

2 Cranin AN: Posterior region Maxilla: a proven implant alternative, dent implan- tol update 3:81, 1992

3 Bodine RL, Yanase T, Bodine A: Forty years of experience with subperiosteal implant dentures in 41 edentulous patients, J Prosthet Dent 75:33, 1996

4 Bodine RL, Melros RJ, Grenoble DE: Long-term implant dentures histology and comparison with previous reports J Prosthet Dent 35:665, 1976

5 Contemporary implant dentistry, second edition Carl E. Misch

6 Bodine RL, Mohammed CI: Histologic studies of a human mandible supporting an implant denture.Part I, J Prosthet Dent 21:203, 1969.

7 James RA: Tissue behavior in the environment produced by permucosal dental devices. In McKinney RV, Lemons JE, editors: The Dental Implants, Littleton, Mass, 1985, PSG Publishing.

8 Berman N. An implant technique for full lower denture. Denture Digest.1951;57:438.

9 Leonard I. Linkow, Jon R. Wagner, Manual Chanavaz: Tripodal Mandibular Subperiosteal Implant: Basic Sciences, Operational Procedures, and Clinical data, Journal of Oral Implantology 1998

10 Leonard I. Linkow, Robe rt Ghalili: Critical Design Errors In Maxillary Subperiosteal Implants journal of oral implantology CLINICAL. 198 Vol. XXIV/No. Four/1998

11 Cranin AN et al: An in vitro comparison of the computerized tomography/CAD- CAM and direct bone impression techniques for subperiosteal implant model gen- eration, J oral implantol 24; 74, 1998.

12 Robert F. Mansueto: Replacement of a Mandibular Subperiosteal Implant, jour- nal of oral implantology Vol. XXV/No. Three/1999

13 Charles M. Weiss, Terry Reynolds: A Collective Conference on the Utilization of Subperiosteal Implants in Implant Dentistry, journal of oral implantology Vol. XXVI/No. Two/2000

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