Oral Health Group
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Restoring the Mandibular Arch with Implant Supported 3-unit Fixed Partial Dentures

June 1, 2007
by Cory Seebach, DMD


ABSTRACT

As a patient’s dental awareness and expectations increase they often seek more comfortable and functional solutions to years spent chewing with removable partial dentures. This situation is encountered quite often where the individual has become frustrated with the ongoing troubles with the removable appliance. Concerns often include sore spots or poor fit, esthetics of retentive arms and metal frameworks, masticatory forces achieved and the appliance continually needing adjustment. The last straw for the lady in this case study was the second abutment tooth which fractured off at the gum line. This case study follows the rational and treatment of replacing a lower tissue-borne removable partial denture (RPD) with bilateral implant supported 3-unit fixed partial dentures (FPD). A couple of cases are depicted illustrating 3-year results of implant and prosthetic stability.

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CASE STUDY

The patient is a female who has worn a mandibular RPD for many years with several complaints and concerns. She presented with the last posterior abutment fractured off and requested a treatment plan which would resolve her problems concerning the ill-fit and poor function of the RPD. Pre-operative models and radiographs were taken. It is the author’s opinion that this is a situation most often resolved with implant supported FPD’s. Although some bone loss was noted intra-orally (bone sounding was carried out) and radiographically, it was determined that no bone grafting was required in order to restore function on both the right and the left. The models were sent for a diagnostic wax up in order to have the surgeon and restorative dentist ensure proper placement of the implants for a successful result.

TREATMENT PLANNING

Treatment planning in edentulous posterior areas requires the patient and doctor to consider many factors in determining the ideal treatment route. Due to advances in bone augmentation techniques, sinus floor elevation and distraction osteogenesis virtually no limits exist to placement of implants.1 Implant retained restorations provide considerable advantages over removable partial dentures. Improved support, a more stable occlusion, preservation of bone and simplification of the prosthesis are a few reasons why implants are the treatment of choice for missing posterior teeth.1 The author also feels it is often more conservative as the adjacent teeth can be spared unnecessary preparation and loading.

The treatment plan should take into consideration the height and width of bone as well as the type of bone. The level of horizontal gingiva compared to the adjacent teeth and the length of time that the area has been edentulous. The major anatomical limitations regarding vessels and nerves must be identified or taken into consideration. The bone in this area in the author’s experience has been found to be excellent quality in most patients. The percentage of integration of the implants is well over 98 percent in the author’s experience. One must also assess the opposing dentition for movement or extrusion which can result in limited interocclusal space for the restoration. The number of implants needed in each area must also be considered. The author’s choice is usually three separate implants or a 3-unit FPD on two solid abutments. The number of implants is dependant on bone quantity and quality.1 Bone quality in this case was excellent and with patient and dentist communication the treatment plan was to place two implants in each edentulous area replacing a total of six teeth with two implant retained 3-unit FPD’s. In treatment planning for the FPD the author chooses between cement and screw-retained prosthesis.

The author most often prefers cemented restorations as it has the benefit of a more esthetic result as occlusal screw holes can be avoided. It is nice to avoid these openings in the smaller more anterior teeth but are often used more posterior. The disadvantages of the cemented restorations involve irretrievability which facilitates individual implant evaluation, soft tissue inspection and modifications.1 The author also prefers the ease of use of the solid abutments and the ability to proceed through treatment with the most similarities to traditional fabrication of a 3-unit FPD including final preparation, impression and lab communication. The author acknowledges that as well as retrievability, the screw retained restorations have the advantages of being able to evaluate implant loading, occlusion, tissue response and screw loosening prior to permanent cementation.2 The author will sometimes choose to cement the final prosthesis with a temporary cement to make retrieval slightly easier if necessary.

TREATMENT

Presurgical

The surgery planned for this patient involved bilateral local anesthesia and placement of four Straumann TE implants. Implants sited were determined by the surgeon using the diagnostic wax-up as a guide with the middle of the implant to line up with the inner incline of the maxillary palatal cusps. A narrower body implant is used to accommodate the slightly narrowed mandibular ridge to ensure complete embodiment of the implant in solid bone.

Surgical placement

The implants chosen to be placed were Straumann TE implants (Fig. 7) (Straumann, Basel, Switzerland) with SLA coating 10mm length and a slightly narrower then ideal width of 3.3mm was chosen due to the narrow mandibular ridge. The surgical kit (Fig. 8) was sterilized and ready for use. Once anesthetized a small crestal incision was made and the surgeon elevated a small flap. A small #4 round bur was used to make a dimple in the implant placement site and a pilot hole was made to a depth of 10mm with copious saline irrigation. Then the series of surgical burs were used to increase the size of the osteotomy to 2.8mm and a final profile drill was used to prepare the bell shaped implant bed according to the neck of the implant. The four burs were used in sequence (Fig. 9) checking the depth intermittently with the depth gauges (Fig. 10) to ensure proper vertical placement of the desired length of implant (Fig. 10).

Optimal implant placement is critical to the esthetic and functional success of implant-supported restorations.3 The Straumann implants were placed with the hand wrench and the surgeon was able to ensure excellent primary stability. The implant height was placed at the gingival crest and healing caps (Fig. 11) were placed. A panoramic radiograph was taken to ensure proper placement and alignment of the implants (Fig. 12). A couple of gut sutures are placed by the surgeon at this point to allow primary closure. The tissue base side of the partial denture was adjusted so as to not put any stress of the healing implants. It was checked with a small amount of bite material (Regisil, Dentsply/Caulk, Milford, DE.) to visualize implant cover screw position (Fig. 13). While it is conceptually possible to successfully load oral implants immediately after their placement in mandibles of adequate density and volume in carefully selected patients, it is still unknown how predictable this approach is.4 The author prefers to let the implant heal for a minimum of six weeks without any loading. Immediate loading of implants placed in the posterior mandible may be a high-risk clinical situation because loading immediately after surgery may result in micro motions at the interface, thus interfering with the healing process.5 The author’s opinion of this may change in the future as some studies are starting to show that “immediate loading of dental implants with 3-unit fixed partial dentures in the posterior mandible can be a safe and predictable procedure.6

Post surgery/healing

Post surgical instructions included having a soft diet for 48 hours and scrupulous oral hygiene and cleansing of the partial denture if it was to be used. The patient was given a one week course of prophylactic antibiotics to take as well as a Chlorhexidine rinse. Specific instruction included ensuring
the cover screws were kept polished to a shine for the entire healing period. Although there was no history of smoking noted by the patient they are still encouraged to cease smoking for a period of at least days 10 days if she was a smoker. The author notes that smokers who abstain from smoking prior to surgery and for 10 days afterward can avoid the complications that are frequently observed in smokers.7

Evaluation was done seven days post surgical and the surgeon noted excellent healing and home care. The patient was scheduled to return in 6-8 weeks for abutment placement and final restorative impressions. When the patient returned in eight weeks for a final impression the implants were evaluated for adequate osseointegration. The patient had no signs of post-operative infection and had no complications in the healing phase. The doctor ensured there was no mobility in the implants and the cover screws were removed. Although little is known on the etiopathogenesis of early failures in achieving osseointegration, they should be viewed as a lack of osteogenic response in relation to endogenous factors (impaired healing) and/or exogenous factors (excessive trauma, infection, premature loading).8

Once the healing caps were removed (Fig.14) the doctor chooses the solid abutments to be used (Fig.15). The doctor then torqued into place 4mm solid abutments using the torque wrench (Fig. 16) to place them with 35N of force. The position and angulations of three of the abutments was ideal (Figs. 17 & 18). It was noted that the implant in the place of the #4.4 needed minor adjustment on the facial aspect to correct the alignment and allow a proper facial profile and emergence of the final restoration (Fig. 19). The final impression was taken with the specially fabricated ‘basket’ and positioning cylinder (Fig. 20) supplied by Straumann placed on the 3.4 and 3.6 implant sites and on the 4.6 implant site which would use the implant analogs in the final restorative lab model. As a result of the adjustment made on the 4.4 implant site two retraction cords were placed in preparation for the impression material to come into direct contact with the adjusted abutment. A bite registration was taken (Regisil, Dentsply/Caulk, Milford, DE.) and appropriate shade matching was noted. All of the information gathered (impression, bite, lab prescription) was sent to the laboratory along with three implant analogs (Fig. 21) to be used in the final stone model for fabrication of the final restorations. The impression techniques illustrate two different final impression techniques which can be used. In the fourth quadrant where the adjustment was made a traditional impression was taken with polyvinyl siloxane material (Reprosil, Dentsply/Caulk, Milford, DE.) showing how simple it is with the solid abutments. The other implants with the plastic basket and corresponding positioning cylinder supplied by the implant company are very simple to use as well. The implants were covered with temporary buttons supplied by Struamman which were fitted into place and cemented with tempbond. These prevented gingival overgrowth while the final prostheses were fabricated.

Insertion

Once the final restorations were returned from the lab they were visually inspected on the models for fit and esthetics (Fig. 22). The model (Fig. 23) shows the implant analogs in place and the one adjusted abutment poured in stone. Intra-orally the temporaries were removed and the implants and abutments were cleaned of cement and rinsed with air and water. The FPD’s were tried in to ensure a passive fit. Until now there is no precise method for determining the accuracy of fit of an implant superstructure in a quantifiable way,9 however, the author will ensure the restoration completely seats with very mild operator pressure. In the author’s experience as well it is noted that ‘the precision of fit which can be obtained through common laboratory and clinical procedures of superstructure fabrication seems to be sufficient enough to produce restorations that do not cause bone damage’9 nor do they result in implant failure due to undue loading forces. Once the fit was established the occlusion was checked to ensure very light occlusion with no excursive interferences present. The restorations needed very minor adjustment and were polished and cemented with a resin-modified glass ionomer (GI) cement (RelyX, 3M ESPE, St. Paul, MN). Zinc Phosphate (ZP) cement is also often used as final cement and the author notes that although less leakage is seen for GI when compared to ZP, other characteristics of resins and resin-modified glass ionomers, such as increased water sorption and expansion over time should be considered when selecting cement.2 Once the cement was set and excess cleaned the occlusion was doubled checked and a final polish was carried out. The anatomy and facial profile of the restorations follow the natural teeth very nicely (Fig. 24).

A final periapical radiograph was taken on each side to ensure complete seating of the restoration and complete removal of hardened cement (Figs. 25 & 26).

FOLLOW-UP

A radiograph and follow-up exam at eight weeks healing shows an excellent result (Fig. 27). The author is confident they possess a wonderful prognosis for long term success. The doctor will monitor the restorations and implants periodically with oral exams and radiographs and the patient will be instructed on the importance of continuing excellent home care consisting of regular brushing and flossing. Two other cases completed by the author are illustrated with radiographs at a three year follow-up showing excellent longer term success. The first case (Fig. 28) is a male patient with a single mandibular FPD three years post surgery showing continued bone integration and height around the implant. The second case (Figs. 29 & 30) is a female patient with very similar bilateral FPD’s illustrating continued excellent bone levels and integration at three years. Both patients experience no sensitivity or discomfort with the restorations or implants and report to be extremely happy with the function and esthetics of the implant supported FPD’s.

CONCLUSION

As the case studies illustrate, the implant supported FPD is a wonderful treatment option to restore posterior missing teeth with or without the presence of a partial denture. The author strongly urges doctors and patients to consider this a primary treatment option for replacing these missing teeth. As well as the considerable functional and esthetic improvements (Fig. 31) the prosthesis will also improve patient self-confidence and overall health (Fig. 32). The patient expressed gratitude to the author stating, “I got to go snorkeling for the first time ever after having the implants replace the denture.” The result also leaves the patient and doctor with very few ongoing problems and much easier maintenance.

Dr. Cory Seebach is a graduate of the University of Saskatchewan in Saskatoon. He has a family private practice in Campbell River, BC with much focus on Cosmetic and Implant dentistry. He is married to Dr. Candice Hall, D.V.M and they live on a hobby farm on Vancouver Island with their 15 horses, 2 dogs, a cat and a parrot.

Oral Health welcomes this original article.

REFERENCES

1.Jirav, S., Chee,W. Treatment planning of implants in posterior quadrants. British Dent J 2006; 201: 13-23

2.Pan, Y., Ramp, L., Lin, C., Liu, P. Comparison of 7 luting protocols and their effect on the retention and marginal leakage of a cement-retained dental implant restoration. The Int J of Oral & Maxillofacial Implants 2006; 21: 587-592

3.Atsu, S. A surgical guide for dental implant placement in edentulous posterior regions. The J of Prosthetic Dent 2006; 96: 129-133

4.Ferrara, A., Galli, C., Mauro, G., Macaluso, G. Immediate provisional restoration of postextraction implants for maxillary single-tooth replacement. The Int J of Perio & Restorative Dent 2006; 26: 371-377

5.Romanos, G., Nen
twig, G. Immediate versus delayed functional loading of implants in the posterior mandible: A 2-year prospective clinical study of 12 consecutive cases. The Int J of Perio & Restorative Dent 2006; 26: 459-469

6.Cornelini, R., Cangini, F., Covani, U., Barone, A., Buser, D. Immediate loading of implants with 3-unit fixed partial dentures: a 12-month clinical study. The Int J of Oral & Maxiilofacial Implants 2006; 21: 914-918

7.Peleg, M., Garg, A., Mazor, Z. Healing in smokers vs. nonsmokers: survival rates for sinus floor augmentation with simultaneous implant placement. The Int J of Oral & Maxillofacial Implants 2006; 21: 551-559

8.Bousdras, V., Aghabeigi, B., Hopper, C., Sindet-Pedersen, S. Management of apical bone loss around a mandibular implant: a case report. The Int J of Oral & Maxillofacial Implants 2006; 21: 439-444

9.Heckman, S., Karl, M., Wichmann, M., Winter, W., Graef, F., Taylor, T. Loading of bone surrounding implants through a 3-unit fixed partial denture fixation: a finite-element analysis based on in vitro and in vivo strain measurements. Clin Oral Implant Res 2006; 17: 345-350


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