Rehabilitation of a maxillary partial edentulous patient using an implant-supported overdenture retained with two bilateral milled bars

Abstract

The use of implants has enabled more treatment options for prosthetic rehabilitation of partially and completely edentulous patients. This clinical report describes a treatment approach for an 80-year-old patient taking advantage of the remaining natural teeth for prosthetic rehabilitation. The final treatment plan included natural tooth-supported and implant-supported crowns combined with a milled bar partial overdenture retained by tilted dental implants. The overdentures supported by the milled bar implants provide the advantages of both fixed and removable restorations. In addition to patient satisfaction, the overdentures also minimise alveolar bone resorption, increase longevity and stability and improve masticatory efficiency.

Background

Rehabilitation of the atrophied edentulous maxilla represents a prosthetic challenge to the clinicians. The design of conventional removable prostheses depends on the amount of remaining alveolar bone and properties, such as retention, stability and support.¹ However, the traditional removable dentures prepared according to specified procedures may not provide adequate comfort and safety to all patients at all times.¹ The anatomical problems also limit the retention of the prostheses especially in cases when only fewer teeth (≤4 teeth) are present. In such cases, implants might be a possibility.

The predictable success of dental implants has made it possible to be used in patients with severe maxillary resorption who frequently face problems retaining the removable partial denture (RPD). Thus they allow them to have an additional treatment option.²

Implant treatment in the context of atrophy may call for sinus elevation and bone grafting.^{3 4} These measures increase the chance that patients rejecting such a treatment because of increased cost, invasive procedure and postsurgical distress. Any prosthesis fabricated to be used in those arches should be aesthetically acceptable, rigid, cost-effective, provide lip support and allow a simple daily oral hygiene maintenance.^3–5

An implant-supported overdenture is a removable denture combined with implants devised to enhance retention and stability for the stomatognathic function, such as smiling, chewing or even clenching. The support of RPDs by implants is an efficient solution for patients with atrophied jaws and prosthetic stability problems.^{1 2} Specifically, such an implant-supported RPD can be an alternative to an ‘unsuccessful’ fixed dental prosthesis. Commonly, removable prostheses have the advantage to facilitate easy oral hygiene procedures, providing better aesthetics and phonetics.⁶ Among the implant-supported overdentures, milled bar type is considered a reliable treatment option for atrophic ridges.^{1 7 8} They have the advantages to gain superior stability, retention, support which allow masticatory ability and patient satisfaction comparable to fixed dental prostheses.¹

The clinician must inform the patients about all available treatment options based on anatomical conditions, prosthesis type, later oral hygiene maintenance, lip support, smile line, costs and duration of treatment.

The clinical report presented here describes a treatment approach for the prosthetic rehabilitation in a patient with an atrophic upper jaw and two remaining second molars and a tilted occlusion plane. Thus, the strategy for an overdenture should reduce the surgical efforts and encompass the remaining teeth combined with two-implant-supported milled bars in hand with an occlusal adaptation of the lower removable prostheses.

Case presentation

An 80-year-old Caucasian male patient presented in the Department of Prosthodontics at the University Hospital of Tubingen, Germany, with the chief problem of discomfort and dissatisfaction concerning his existing maxillary denture. A comprehensive medical and dental history along with panoramic radiograph (orthopantomogram (OPG)) were obtained, and they did not present with any pathological findings. Intraoral examination revealed poorly adapted, and an aesthetically compromised maxillary denture supported by two posterior teeth with telescopic crowns (figure 1A, B). The lower jaw was provided with a telescopic removable denture on five anterior abutment teeth. The occlusal plane was rotated cranially and therefore not parallel to the Camper plane.

Figure 1.

Intraoral photograph of the patient (A) poorly adapted maxillary denture and (B) upper jaw with telescopic crowns on the remaining natural teeth.

The treatment plan based on patient’s complaints, clinical and radiographical examinations included implant-supported bar-retained maxillary overdenture with two telescopic hybrid double crowns as posterior abutments in hand with a technical adaptation of the existing telescopic denture in the lower jaw.

Surgical intervention

The diameter and length of the implant were determined by OPG obtained using the metal ball references (diameter=5 mm) integrated into a vacuum moulded foil at the regions of teeth (FDI-scheme) 14, 12, 22, 24.

The patient received prophylaxis antibiotic 1 day before the surgery (clindamycin, 300 mg) to reduce the risk of postoperative infection. Surgery was carried out under local anaesthesia using 2% Ultracain D-S forte 1.8 mL with epinephrine (1:100 000). A full-thickness flap was prepared to exhibit the topography of the remaining bone. Four dental implants (BEGO Semados SCX 58260, BEGO Implant Systems GmbH, Germany) with a diameter of 3.75 and 10 mm in length were placed according to the bone situation at the region of 14, 24, 12 and 22. The posterior implants were placed with an angulation in accordance with the anterior wall of the sinus, and bone substitutes (Bio-Oss Geistlich Pharma AG, Wolhusen, Switzerland) were placed at the buccal site of left first premolar region. All implants had a final torque of 45 Ncm with good implant stability (see figure 2a). The healing caps were placed, and the flap repositioned and the suture was placed using Vicryl TM 3.0 (Ethicon R, Johnson & Johnson Medical NV, Belgium). An OPG was taken to cross-check the position of the implants (see figure 2b).

Figure 2.

(A) Implants placed in situ and (B) postoperative intraoral panoramic radiograph confirming the position of the implants.

The patient was instructed not to wear his denture and to presume the antibiotic medication (clindamycin 300 mg) for a further 5 days. Ibuprofen 400 mg was recommended to reduce postoperative pain two times per day for 3 days. The sutures were removed 8 days after the surgery. The denture was adapted and relined with soft silicon relining material (Mollosil Plus, DETAX GmbH, Ettlingen, Germany) in order to be further worn during the period of implants osseointegration. This was determined to be 6 months due to the implementation of bone substitutes as well as the recommendations for the healing period in the upper jaw.⁹

Prosthetic intervention

The second stage of minor surgery was performed after 6 months of osseointegration. The absence of pain, no clinical mobility, infection and gingival bleeding determined the degree of osseointegration. In a second surgical procedure, a semilunar incision over the palatal half of the estimated implant head was performed under local anaesthesia. A tissue biopsy punch was used to differentiate the shape of the incision with the application of light pressure over the tissue.

The implant was exposed by removing the cover and the healing abutments (3.5–5.0 mm in diameter) were then placed over the implants. There was no need for sutures at this stage.¹⁰ The old prosthesis was relined with tissue conditioner and the patient was recalled after 3 weeks.

After 3 weeks, the old posterior metal crowns were removed, the preparation of the teeth were refined to allow the marginal fit of hybrid double crowns. Four impression copings were placed on the implants after removing the gingival formers. A customised acrylic resin tray (Zeta Tray LC, Zhermack GmbH, Germany) was fabricated on the gypsum cast delivered by the alginate impression. A pick-up coping impression was made with polyether impression materials (Impregum Penta, and Permadyne light-bodied, 3M Deutschland GmbH, Germany) in a double mixing technique. The provisional bite registration was recorded with putty silicon material (Silaplast, DETAX GmbH).

Specifically, the horizontal and vertical maxillomandibular records were obtained with the old relined dentures initially and found suitable with regard to the thirds of the face. The soft-pogonion and subnasale were marked with a dot and the distance measured. This situation of vertical dimension was recorded with a putty polyvinyl siloxane elastomer (Silaplast) covering both dental arches while controlling the distance between the skin markers. Based on this jaw relation, a custom maxillary registration tray with wax bite blocks made from light curing resin (Zeta Tray LC, Zhermack GmbH), was ordered from the dental lab.

In the next visit, the two primary copings of the molars were tried on and checked for marginal fit. The implant abutments were delivered in separated sets of two. These were connected intraorally with a resin (Pattern Resin, GC America, Illinois, USA). Again, a customised tray with perforations was applied (pick-up technique) in double mixing technique with polyether material (Impregum Penta/Permadyne light-bodied, 3M ESPE, Seefeld, Germany) to fabricate a cast. The casts were mounted on the articulator using a provisional jaw relationship. A bar retainer was divided into two portions due to the angulation of the posterior implants.

The fit of the crowns # 17 # 27 was evaluated, and following removal of gingival formers from the top of the implant, the original abutments were screwed in with 20 Ncm torque. Each block of segments was screwed on top of the implant abutments. The abutments and the individual segments were affixed with pattern resin in the patient’s mouth. Definitive pick-up impression with second customised special impression tray over the splinted implants was made using a polyether impression material. After the setting of impression material, all the screws were loosened, and the impression was carefully removed from the mouth to avoid damage.

The final maxilla–mandibular relation in vertical and horizontal dimension was recorded with the telescopic denture in the lower and the wax blocks of the custom tray in the upper. A face-bow transfer to a semiadjustable articulator (Artex System, Amann-Girrbach, Pforzheim, Germany) allowed the positioning of the casts with the help of the registration tray (figure 3).

Figure 3.

Face-bow transfer for mounting to the articulator.

Once the jaw relation had been recorded, the bite index was created on the preliminary cast. Primary crowns were placed, and the bite block held in place by screws secured into two-implant, and the adjustment was achieved according to the lip support. Here it was noticed that the occlusal plane was not parallel to the Camper’s line in the sagittal axis. The occlusion plane was corrected in wax-up try-in, and the shade of the tooth was selected.

In the next step, the wax-up try-in was done in the patient mouth in order to check for the function and aesthetics, and for the proper alignment of the anterior teeth before the milled bar retainer was designed. Bilateral balanced occlusion scheme was followed for teeth arrangement.

The prosthesis framework try-in with two swivel ledges, two separated milled bar retainers and crowns with friction pins were fabricated (figure 4). The occlusal plane was slightly elevated as instructed by the clinician. The bilateral bars were screwed over the implant abutments. Sheffield test was performed on the milled bar, and the fitting was optimum. In this test, the framework is seated onto the implants and one screw is tightened lightly and discrepancies are observed at the other terminal screw. The screw should not resist the tightening process.¹¹ The fitting of the framework try-in prosthesis was evaluated in the patient mouth. The upper occlusion plane was checked on both sides and parallel to the Camper plane. The upper anterior teeth were marked for needed modification according to the smile line. The posteriors were in 3 mm distance to the lower as the situation was in the articulator to overcome the tilt of the occlusal plane.

Figure 4.

(A) Bar retainer on the definitive cast; (B) framework try-in on the bars.

Delivery appointment

Figure 5 presents the final intraoral situation of the patient with implant and attachments in situ and the internal fitting surface of the overdenture. Upper original abutments were screwed on the implants with a torque (30 Ncm) applying 1% chlorhexidine gel into the screw channel, and two separated milled bars were screwed on implant abutments. The hybrid double crowns were cemented using zinc phosphate cement (Harvard Cement, Harvard Dental International GmbH, Germany). The occlusion was recorded with a beautiful pink wax plate bite registration in order to mount a gypsum cast of the ‘new’ upper overdenture to the existing telescopic denture in the lower within a semiadjustable articulator. The posteriors of the lower denture were modified with a light-curing resin (Sinfony, 3M Deutschland GmbH) to ensure static and dynamic occlusion. Figure 6 presents the pretreatment and post-treatment photographs of the patient and the appliance.

Figure 5.

(A) Final intraoral situation with implant and attachments and (B) internal surface of the overdenture with the counter bar and the attachments.

Figure 6.

Pretreatment (A–D) and post-treatment (E–H) photographs of the patient; (A, E) presents the lateral view of the patient with the appliance in place, (B, F) presents the aesthetic smile zone of the patient with the appliance, (C, G) presents the intraoral photograph of the appliance, (D, H) presents the intraoral frontal view of the maxillary and mandibular appliance in occlusion.

Outcome and follow-up

• At the recall visit at 6 months, sound situations of the soft tissues were observed and there was no signs of bleeding.

• Oral/prosthesis hygiene was maintained well.

• The patient was delighted and satisfied with the implant-retained maxillary overdentures compared with his old conventional telescopic maxillary overdenture.

A standard OPG with the implants bars was obtained for forensic reasons as stipulated by German law (figure 7). Postdelivery instruction was given to the patient regarding prosthesis placement, removal and cleaning. Specifically, the cleaning of the milled bars with superfloss and the intaglio surfaces of the overdenture with a toothbrush. At the 1 week check-up visit, the prosthesis was evaluated, and the patient had no complaint. No plaque was detected on the bar or prosthesis. The patient was informed to maintain the hygiene measures and to show up for a recall visit after 6 months.

Figure 7.

Postdelivery intraoral panoramic radiograph of the patient.

Discussion

In the current case, considering the remaining natural teeth and the condition of maxillary bone it was planned to treat the case with tooth and implant-supported hybrid double crown combined with a milled bar partial overdenture.

One treatment option would be a remake of the prosthesis with regard to the occlusal set-up of artificial teeth. This would have not allowed an improvement of retention and it would have necessitated the coverage of the palate by the basis of the overdenture denture. In palatal coverage by a complete denture, the oral environment is altered because of the less space available for the tongue which could affect the masticatory function, speech and disturb sensorimotor function.¹² The removable overdenture is much similar to the form of the complete dentures, whereas the bases of the fixed prosthesis are usually narrower, which could overcome some of the problems of speech adaptation observed with fixed prosthesis.¹³

The other treatment option would have been fixed implant-retained prosthesis. This would have been only possible by the insertion of at least eight implants and an intensive surgical approach, including a sinus lift at a region of the first upper molars (see OPG). Furthermore, a fixed restoration would not allow sufficient support of the upper lip and sophisticate the hygiene measures. This is important to mention since the patient is 80 years and manual as well as visual competence is reduced and is expected to be compromised within the next decade.

The implant-retained milled bar overdenture presents with conically aligned one or two milled bars. The alignment ranges from 2 to 10 grades. The removable overdenture is then accurately and rigidly adapted to the bar, thereby limiting rotational and lateral movements. The rigid anchorage system evenly distributes the stresses due to different forces along with the implant-overdenture complex. Additionally, the overdenture contains fastenings that minimise the movement along its path of insertion. The retention is achieved by friction between the bar and counter bar in the overdenture and the fastenings.^{6 13–17}

The prosthesis was incorporated with two swivel latch, a passive action element used to lock the denture. This gives the patient the feeling that the prosthesis is fixed and it will not come out.¹⁸ This attachment can be removed in the long run when manual dexterity is reduced. Even then enough retention could be obtained by friction pins within the superstructure.

The implant-supported milled bar overdenture compared with the implant mucous supported overdenture, presents several advantages including limiting bone resorption, extending the life of the attachments, less prosthetic complications and maintenance needs.^{6 16 17}

In the current case, the spark erosion technique was used for refining the implant-supported superstructure. Spark erosion provides an excellent fit that ensured retention, stability and support similar to that of a fixed prosthesis.¹⁹ However, misfits between the bar and the implants might introduce constant stress to the implants after screw tightening. This strains on the implant-bone connection will consequence in a bone loss at the implant site. Thus, the Sheffield test evaluates the ‘passivity’ of the bar screwed on two or more implants. The non-passivity of the implants and/or the prosthesis may cause mechanical failures thereby adversely affecting the surrounding gingiva.²⁰ In the present case, the Sheffield test showed that the fit was optimum.

The telescopic hybrid double crown with a friction pin used as in this case presents advantages, including the reduction of the luted primary crown to provide more space for the secondary crown for aesthetic and hygienic purpose. Furthermore, the pin allows a later adjustment of retention and even a repair if broken.^{21 22}

The limitations of these type of treatment and prosthesis includes critical treatment planning for positioning and placement of implants, and technique sensitive fabrication techniques. The patient was informed to maintain good oral hygiene and to have a regular follow-up.

Patient’s perspective.

I am quite happy with this prosthesis. Even if the prosthesis is removable, it offers a secure fit and setting—just like my ‘own teeth’. In particular, the uncovered roof of the mouth allows me to enjoy food more sensitive and to pronounce more clearly and distinctly than with the plastic denture I had before.

Learning points.

• The tooth and implant-supported overdenture retained by a milled bar allows the clinician to overcome particular problems associated with the treatment of maxillary arch using implants.

• Also, the use of telescopic crowns compared with conventional removable partial dentures has several advantages such as good stability and retention, stable occlusion and enhanced masticatory efficiency due to the controlled sensory feeling.

• This promises a long-term solution for the elderly especially regarding oral hygiene and stable oral health and quality of life.