One-Piece Root-Form Implants: A Return to Simplicity

The concept of loading dental implants immediately after placement, while currently viewed as novel and even groundbreaking, in fact is not new. Blade-type implants were being placed by the author and other clinicians at least as far back as 1970. Such designs incorporated an integral abutment that was immediately placed in function. When used in sites containing bone that enabled the achievement of good primary stability (Types I and II), blade-style implants often survived for long periods of time.1 However, placement in softer (Types III or IV) bone that afforded less stability often led to fibrous tissue encapsulation, soft-tissue change, bone loss, and eventual implant removal.2 

By the mid-1970s, several developments held the promise of avoiding such problems. Ceramic 1-piece root-form implants included synthetic sapphire (eg, Bioceram Single Crystal Sapphire, Kyocera Corp, Kyoto, Japan) as well as aluminum oxide (eg, Miter Synthodont, Miter Inc, Columbus, Oh). Although the ceramic materials were biocompatible and fostered excellent osseointegration, they were also brittle and frequently broke.3 

Performance of the Swiss TPS Screw 1-piece implants was better over time.4 These implants were utilized in edentulous mandibular cases. The protocol called for placing 4 implants into the anterior mandible between the mental foramena. Impression copings were placed on the implant abutments, and an impression was taken. The copings were incorporated in the impression, and analogs were seated into the copings. A model was fabricated and sent to the dental laboratory to construct a connecting bar for next-day delivery to the patient. The bar was fastened to the 1-piece TPS Screw implant with retaining screws. An overdenture was fabricated and retained by the bar and attachments.

Another alternative arose in the form of two-piece root-form titanium implants (eg, Miter Titanodont, Miter Inc; Branemark, Nobel Biocare, Yorba Linda, Calif). Branemark5,6 asserted that the best way to achieve osseointegration was to place titanium implants atraumatically and submerge them below the mucosa, allowing them to heal out of function before connecting any transgingival components. The successes documented when using this approach eventually convinced many clinicians that it was the only acceptable protocol.

Many 1-piece implants nonetheless survived long term. At the same time, evolution of the science of implant dentistry yielded technological breakthroughs, including improved implant-threading patterns and surface treatments that have demonstrably fostered greater primary stability and faster healing.7 As a consequence, a number of practitioners in recent years have once again begun to place implants in a 1-stage procedure by allowing the implants' coronal portions or healing collars to protrude through the soft tissue.8 This avoids the need for a second surgical exposure to expose the implant.

Excellent success rates have been documented with this approach,9–13 including numerous cases in which the single-stage placement has been accompanied by attachment of a fixed provisional prosthesis placed in function, at least to some extent. However, most clinicians have continued to utilize 2-piece implant systems for 1-stage procedures, even though those designs were never intended for use in this manner. The implant-abutment juncture constitutes a structural weakness, while the need to remove a healing abutment and replace it with a final abutment adds complexity to the procedure and insult to the healed or healing gingiva.

The 1-piece implant utilized in the following cases avoids both drawbacks.

The implant (NobelDirect, Nobel Biocare) is machined from a piece of titanium that incorporates both the implant body and an integral fixed abutment in a single component. It is available in 3 diameters (3.5, 4.3, and 5 mm) and 3 lengths (10, 13, and 16 mm). A 3.0-mm-diameter implant is also manufactured for use in confined spaces in the region of the mandibular central and lateral incisors and maxillary lateral incisors (Figure 1).

The implant has an anodized surface (TiUnite, Nobel Biocare), created through a controlled increase of the titanium oxide layer. The resulting increased oxide thickness and roughness, along with the porous structure, result in an enlarged surface area that has been demonstrated to promote osseointegration to the alveolar bone (Figure 2).14 The anodized surface extends beyond the threads and onto the abutment portion of the implant. A recent study has shown that the junctional epithelium effectively attaches via hemidesmosomes to the surface, much as it does to natural teeth.15 The connective tissue interposed between the junctional epithelium and the alveolar crest is dominated by both circumferentially and longitudinally running collagen fibers.15 As a result, the connective tissue around TiUnite implants is stable and healthy (Figures 3 and 4).

The following cases illustrate the use of this 1-piece implant system.

The patient, a 48-year-old female, presented with nonrestorable mandibular left first and second bicuspids. She was also missing the mandibular left first and second molars and the mandibular right first and second bicuspids and first molar. Her opposing dentition consisted of a fixed prosthesis supported by 10 implants.

The treatment plan called for extraction of the 2 bicuspids, followed by immediate placement of two 4.3-mm-wide by 13-mm-long implants into the extraction sockets. At the same time, 4 additional implants were to be placed in the areas of the mandibular left second molar and mandibular right first and second bicuspids and first molar.

Infiltration anesthesia was administered on the buccal/lingual aspects of the teeth to be removed, as well as the edentulous area. The bicuspids were atraumatically extracted. The 2-mm pilot drill was utilized at each extraction site to a depth of 1 to 2 mm deeper than the teeth being replaced.

Site preparation then continued, using 3.5- and 4.3-mm tapered drills, followed by a bone tap. Two implants were placed into the extraction sites at 35 rpm and 45 Ncm of torque. This was confirmed with a manual torque wrench.

A flapless surgical technique was used to prepare the remaining sites, except for the mandibular first molar, which was to be a pontic. At each site, a drill guide was positioned and a twist drill was employed to penetrate to approximately 10 mm deep. Use of the drill guide revealed the exact angulation and position that would be achieved when the implant was placed (Figure 5).

At each site, the drill guide was then removed and a tissue-punch guide was inserted into the pilot hole. The 4.3-mm tissue punch was placed over the supragingival portion of the tissue-punch guide and used to cut through the soft tissue down to the crest of the ridge, creating a series of tissue plugs. Each was released from the alveolar crest with the aid of a curette scaler (Figure 6).

After further site preparation with a 4.3-mm tapered drill, implants (4.3 mm × 13 mm) were placed in the sites of the mandibular left second molar and the 2 right bicuspids. A 5.0-mm-wide by 13-mm-long implant was placed at the site of the mandibular right first molar. All 4 implants were tightened to 45 Ncm. At the two extraction sites, the abutment portions of the 2 implants placed there were prepared with a high-speed carbide bur and finished with a high-speed tapered diamond drill and copious amounts of water. No preparation of the abutment portions of the other implants was necessary.

The patient closed in centric relation occlusion to confirm the presence of sufficient interocclusal space. Fixed acrylic provisional restorations were then fabricated and seated over each of the 6 implants. Care was taken to ensure that the margins of the provisionals did not impinge on or irritate the soft tissue. The occlusion was also adjusted to minimize any contacts (Figure 7).

Two and a half months later, the temporary restorations were removed. Radiographic examination confirmed that the implants were well integrated. The soft tissue around the cervical margins was firm and healthy in appearance (Figures 8 and 9).

Definitive margins were prepared on all the abutments, and direct impressions were recorded with a medium-bodied addition silicone impression material. Interocclusal bite registrations were taken, and the impressions were sent to the laboratory for fabrication of a ceramic-metal fixed prosthesis. Three-and-a-half months after implant placement, the final restorations were placed (Figures 10 and 11).

The patient was an 18-year-old male with congenitally missing maxillary right and left lateral incisors. The treatment plan called for placement of two 3.0- × 15-mm implants along with immediate fixed temporary crowns. The implant diameters and lengths were determined using both radiographs and a bone caliper that engaged the facial and lingual bone through the soft tissue under anesthesia (Figure 12).

A 1.5-mm twist drill was inserted into a 3.0-mm drill guide and utilized to penetrate the bone to a depth of approximately 8 mm (Figure 13). When it was clear that the implant angulation would be satisfactory, the 3.0-mm tissue-punch guide was inserted into the pilot hole and a 3.0-mm tissue punch was used to create a circular sulcus.

The site was then entered with a 2-mm pilot drill to a depth of 15 mm, followed by utilization of a 2.5-mm drill. The implant was placed using a 3.0-mm implant driver (Figure 14). The same procedure was followed on the right side (Figure 15).

The abutment portions of the implants were prepared to achieve interarch clearance. Provisional crowns were then fabricated and checked carefully to ensure there were no contacts in centric relation occlusion nor in any other excursions. The crowns were cemented (ImProv, Nobel Biocare) (Figure 16) and radiographs were taken (Figure 17).

Three months later, the provisional crown was removed and the abutment was further prepared to establish a margin for the final restoration. An impression was taken and sent to the laboratory, where a ceramometal restoration was created. This was delivered and cemented (ImProv).

A 50-year-old male patient presented with a fractured endodontically treated mandibular left second bicuspid. Under local anesthesia, the root fragments were carefully removed, and the site was prepared to a depth of 13 mm, roughly 1.5 mm deeper than the tooth being replaced. After further site preparation, an implant (5- × 13-mm) was placed, taking care to leave the anodized surface of the neck above the crestal bone and in apposition to the soft tissue. Initial stability was assessed to be 45 Ncm.

Although the interocclusal space between the top of the abutment portion of the implant and the opposing teeth was found to be sufficient, the abutment circumference was minimally reduced utilizing a titanium metal-cutting bur in a high-speed handpiece, with copious amounts of water. A provisional restoration was placed and adjusted so that it was out of occlusion by at least 1 mm in all excursions. It was then cemented (ImProv).

After 10 weeks, the provisional crown was removed and the abutment portion of the implant was modified to conform to the gingival margin of the soft tissue. An impression was made with an addition silicone material and sent to the laboratory for fabrication of a ceramometal restoration.

Ten days later, the final restoration was delivered and checked for marginal integrity, fit, and occlusion (Figure 18).

A 52-year-old female presented with a missing right mandibular first molar. Because the 2 adjoining teeth were healthy, the patient was averse to replacing the missing tooth with a fixed bridge.

Examination revealed the site of the missing tooth to be approximately 8 mm wide, with the distance from the alveolar crest to the inferior alveolar nerve 15.5 mm. The presence of adequate amounts of keratinized tissue made a flapless surgical technique feasible, and the treatment plan called for placement of an implant (5 × 13 mm).

The site was prepared, utilizing a 2-mm pilot drill with a 5-mm drill guide (Figure 19), followed by a 5-mm tissue-punch guide and 5-mm tissue punch. Because the bone was judged to be between Type II and Type III, no thread former was utilized. Instead, it was decided to self-thread the implant to ensure stability at 45 degrees (Figure 20).

In this case, the patient opted against placement of a temporary restoration. After a 3-month healing interval, an impression was recorded and bite registrations were taken. The laboratory then fabricated a zirconia coping (Procera, Nobel Biocare) and an all-ceramic crown.

At the time of delivery, occlusion was carefully checked and the restoration was cemented (ImProv) (Figures 21 and 22).

The implant system performed well for 1-stage implant placement. However, excessive occlusal loading can still compromise results. In the experience of the author, keeping the implant at least 0.5 mm out of occlusion in all excursions has proven to be a prudent guideline. That dimension should be increased to 1 mm when using the 3.0-mm-diameter implant. Similarly, patients should be advised to avoid any forceful chewing in the vicinity of the implant(s); compliance is essential.

Whenever adequate keratinized tissue and bone are available, a flapless procedure is recommended. The benefits of this approach include reduced postoperative swelling and discomfort, minimal bleeding, and elimination of the need for any stitches. Avoidance of a surgical flap reflection also maintains a better blood supply to the site, reducing the likelihood of resorption,16 as well as making it more predictable to achieve optimal postoperative esthetics. In the author's experience, 7 mm or more of keratinized tissue in the buccal/lingual dimension is ideal.

The importance of achieving primary implant stability likewise cannot be overestimated. Final tightening torque should fall within the range of 35 to 45 Ncm.17,18 If sufficient stability is not attainable, the implant should be removed and a conventional implant and transmucosal healing abutment should be placed and allowed to heal before further restorative measures are taken.

When a flapless placement procedure is being utilized, careful attention should be paid to the drilling technique. To prevent the internal irrigation holes from becoming plugged with bone, an in-and-out motion should be employed, along with continuous irrigation.

In all the cases reported here, primary stability was easily achieved and osseointegration was subsequently confirmed (Figure 23). Because the surgeries were minimally invasive, patients reported little or no discomfort and all expressed enthusiasm for the excellent esthetic results achieved. Use of the 1-piece implant also significantly shortened treatment time due to the elimination of postsurgical visits traditionally required to remove the healing abutment and place a permanent abutment.

The author has a clinical consulting agreement with Nobel BioCare for ongoing clinical studies and continuing education courses.