two-piece titanium implants

Gingival esthetics around natural teeth is based upon a constant vertical dimension of healthy periodontal soft tissues, the Biologic Width. When placing endosseous implants, however, several factors influence periimplant soft and crestal hard tissue reactions, which are not well understood as of today. Therefore, the purpose of this study was to histometrically examine periimplant soft tissue dimensions dependent on varying locations of a rough/smooth implant border in one-piece implants or a microgap (interface) in two-piece implants in relation to the crest of the bone, with twopiece implants being placed according to either a submerged or a nonsubmerged technique. Thus, 59 implants were placed in edentulous mandibular areas of five foxhounds in a side-by-side comparison. At the time of sacrifice, six months after implant placement, the Biologic Width dimension for one-piece implants, with the rough/smooth border located at the bone crest level, was significantly smaller (P!0.05) compared to twopiece implants with a microgap (interface) located at or below the crest of the bone. In addition, for one-piece implants, the tip of the gingival margin (GM) was located significantly more coronally (P!0.005) compared to two-piece implants. These findings, as evaluated by nondecalcified histology under unloaded conditions in the canine mandible, suggest that the gingival margin (GM) is located more coronally and Biologic Width (BW) dimensions are more similar to natural teeth around one-piece nonsubmerged implants compared to either two-piece nonsubmerged or two-piece submerged implants. In 1921, Gottlieb initially described the ‘‘epithelial attachment’’ around a natural tooth by covering distinct areas of the enamel surface or the cementum and not by just being attached to the cemento-enamel junction at a certain point or level, respectively (Gottlieb 1921). Later on, these findings have been confirmed (Orban & Mueller 1929), and in addition, the ‘‘gingival crevice’’ or sulcus has been defined. Subsequently, Feneis showed that connective tissue consists of three-dimensionally oriented fibers firmly connecting tooth structures to the surrounding gingiva (Feneis 1952). Thus, it became clear that both epithelial as well as connective tissue attachment contribute to a ‘protection mechanism’ in a most challenging area where the natural tooth penetrates the ectodermal integrity of the body. Sicher confirmed these findings in 1959 and called this functional unit the ‘‘dentogingival junction’’ (Sicher 1959). In 1961, Gargiulo et al. found out that the vertical dimension of the dentogingival junction, comprised of sulcus depth (SD), junctional epithelium (JE), and connective tissue attachment (CTA), is a physiologically formed and stable diHermann et al . Biologic Width around oneand two-piece titanium implants mension, subsequently called ‘‘Biologic Width’’, and that this unit forms at a level dependent on the location of the crest of the alveolar bone (Gargiulo et al. 1961). Taking these biological principles into consideration, two major clinical procedures have been derived from these findings and are widely used today, one being the ‘‘forced eruption’’ (Ingber 1976) and the other one being the ‘‘surgical lengthening of the crown’’ (Ingber et al. 1977). Both procedures are based upon the understanding that changing the level of the alveolar bone will move the complete dentogingival junction as a unit on a predictable basis towards the same direction (apically or coronally, respectively). These procedures have great impact as to the location of the gingival margin (tip of the papilla) and, therefore, provide a major tool to achieve stable and esthetic gingival harmony around a healthy natural crown or a tooth-borne restoration. In the early years of implant dentistry, research mainly focused on hard tissue integration. Based upon positive longterm results with implant-borne fixed partial dentures as well as overdentures using submerged as well as nonsubmerged implants (for review see Cochran 1996), implant-borne single tooth restorations became more and more popuFig. 1. a. Schematic (true to scale) of implant whereas the dashed line shows the location of (Cochran et al. 1997; Hermann et al. 2000a). The types A–C at time of implant placement in rethe microgap (interface). Note that all three types dark red compartment indicates the vertical dilation to soft tissues and bone. Soft tissue dimen(A–C) were inserted according to a nonsubmension of the sulcus depth (SD), the pink comsions are adapted from the literature (Cochran et merged approach. Implant types A and B are onepartment the junctional epithelium (JE), and the al. 1997; Hermann et al. 2000a). The dark red piece implants exhibiting no microgap (interyellow compartment the connective tissue concompartment represents the vertical dimension face), while type C implants are two-piece imtact (CTC). Note that all these implants were of the sulcus depth (SD), the pink compartment plants with a microgap (interface) located at the placed using a submerged technique. Implant the junctional epithelium (JE), and the yellow bone crest level. b. Schematic (true to scale) of imtypes D–F are two-piece implants with a compartment the connective tissue contact plant types D–F at time of implant placement in microgap (interface) located at different levels in (CTC). The solid black line delineates the borrelation to soft tissues and bone. Soft tissue direlation to the crest of the bone. der between rough and smooth implant surface, mensions are adapted from the literature 560 | Clin. Oral Impl. Res. 12, 2001 / 559–571 lar during the 1990s. As a consequence, increasing attention was given to study periimplant crestal bone as well as soft tissue reactions. Thus, Berglundh and coworkers (Berglundh et al. 1991; Berglundh & Lindhe 1996) and Abrahamsson and collaborators (Abrahamsson et al. 1996; Abrahamsson et al. 1997; Abrahamsson et al. 1999) presented histometric data on two-piece, submerged as well as nonsubmerged implants. Cochran et al. (1997) and Hermann et al. (2001) first published periimplant histometric results based upon an experimental study analyzing and confirming the Biologic Width dimensions around a natural tooth with those around a onepiece, nonsubmerged implant. This same research group also compared crestal bone reactions around oneand two-piece titanium implants placed according to a nonsubmerged or submerged technique in a side-by-side comparison (Hermann et al. 1997; Hermann et al. 2000b, Hermann et al. 2001), showing significant changes in crestal bone reactions dependent on the implant design and/or technique used (one-piece vs. two-piece implant; nonsubmerged vs. submerged approach), which, in part, has also been confirmed in a series of case reports involving 11 patients (Hämmerle et al. 1996). The purpose of this study was to analyze the dimensions of the Biologic Width around implants of varying designs: onepiece implants with a rough/smooth border vs. two-piece implants with a microgap (interface) as well as surgical technique used (nonsubmerged vs. submerged). In addition, the relationship of the gingival margin (GM) to the implant was of particular interest since its location and stability is important for periimplant soft tissues, and the resulting esthetics of the implant-borne restoration. Material and methods Implant design and surfaces All six different experimental implants (types A-F; Figs la, lb) were based on a cylindrical full-body screw design and were made from cold-worked, grade-IV commercially pure titanium (Institut Straumann AG, Waldenburg/BL, Switzerland). The outer diameter (thread tips) measured 4.1 mm, whereas the inner diameter was 3.5 mm at a total length of 9 mm. The coronal portion of each onepiece implant and the abutments in twopiece implants consisted of a machined, relatively smooth titanium surface. The apical part of each implant had a sandblasted (large-grit) and HCI/H2SO4 acidetched surface (SLA) with two levels of roughness, one at 20–40 mm peak to Hermann et al . Biologic Width around oneand two-piece titanium implants peak, and a superimposed second one at 2–4 mm peak to peak. The apical, rough portion (SLA surface) of type A implants was 6.0 mm in length with the rough/smooth implant border clinically placed at the alveolar crest. Type B implants had a 5.0 mm long SLA portion, with the rough/smooth border placed 1.0 mm below the crest. For all other implants (types C-F), the rough implant surface (SLA) was 4.5 mm in vertical dimension with the rough/smooth implant border located about 1.5 mm below the crest (Figs 1a and 1b). Type A and B implants were one-piece implants without a microgap (interface) present, while implant types C-F consisted of two pieces, with a clinically relevant microgap (interface) of about 50 mm in size (Binon et al. 1992; Keith et al. 1999) between the implant and the secondary component, the abutment. The location of the microgap (interface) was defined to be clinically at the bone crest level for types C and D, however, for types E and F, the microgap (interface) was located 1 mm above or 1 mm below the crest, respectively. Implant types A-C were placed according to a nonsubmerged technique, whereas types D-F were inserted using a submerged approach. Study animals For this study, five lab-bred, male American foxhounds were used. Prior to the start of the experiment, the protocol was approved by the ‘Institutional Animal Care and Use Committee’ of the University of Texas Health Science Center at San Antonio (UTHSCSA). The dogs were approximately two years of age at the beginning of the study and had a body weight of about 30–35 kg. None of the Fig. 2. Study design. 561 | Clin. Oral Impl. Res. 12, 2001 / 559–571 dogs had heart worms and all of them were quarantined before the experiment was started. Surgeries – Extraction The extraction technique removing all mandibular premolars and the first molar bilaterally has already been described in detail and published recently (Hermann et al. 1997; Hermann et al. 2000b). Surgeries – Implant placement Nonsubmerged and submerged implants (types A–F) were placed after a healing period of 6 months (Fig. 2), under the same surgical conditions as tooth extraction had been performed (operating room, anesthesia, sterility). A crestal incision was performed maximizing keratinized gingiva on each side of the incision. Fullthickness flaps were carefully reflected on the lingual and buccal aspect. Foramina mentalia were dissected and exposed. The edentulous osseous ridge was carefully flattened utilizing an acrylic bur combined with copious irrigation with chilled sterile physiologic saline. Measurements were made using a boley gauge to help distribute six test implants on each side of the mandible. Implant site preparations were carried out with lowtorque reduction rotary instruments at 500 rpm using chilled saline. Implant types A–C were placed according to a nonsubmerged approach (Fig. 1a), i.e. for type C, implants and abutments were screwed together at the time of first-stage surgery. Implant types D–F were placed according to a submerged technique (Fig. 1b). Finally, one of each kind of test implant was placed per side in a randomized fashion. Thus, no implant type had a biased position in the arch. Periosteal relieving and contouring incisions were carried out on the buccal and lingual aspects of each implant in order to obtain tension-free adaptation of the wound margins for close adaptation of the gingiva to the transgingival portion of the nonsubmerged one-piece implants (types A and B), and the abutment of type C implants. Wound closure over the submerged implants (types D–F) was achieved using horizontal mattress combined with interrupted sutures. At the day of surgery, the dogs received 20 mg NubainA (nalbuphine 10 mg/ml – Astra Pharmaceutical Products Inc., Westborough, MA, USA) s.c. BID. Three ml PenBA (benzathine penicillin 150,000 I.U. combined with procaine penicillin G 150,000 I. U. – Pfizer Inc., Lee’s Summit, MO, USA) were given s.c. SID every 48 h for 14 days. On day 1, 100 mg of the antibiotic GentocinA (gentamicin 50 mg/ml – Schering-Plough Animal Health Corp., Kenilworth, NJ, USA) were administered s.c. BID, and the same amount SID from day 2–10. To reduce swelling, the foxhounds received 2 ml of the antiinflammatory DexajectA (dexamethasone 2 mg/ ml – Burns Veterinary Supply, Oakland, CA, USA) i.m. SID day 1 and at day 4. Suture removal was carried out after 7–10 days as described above. To minimize loading, the animals were fed a softened diet for the duration of the study. Mechanical and chemical plaque control was carried out three times per week, using a soft toothbrush and a soft sponge in combination with PlakOutA Gel (chlorhexidine digluconate 0.2% – Hawe-Neos AG, Bioggio/TI, Switzerland). Surgeries – Abutment connection Second-stage surgery was performed three months after implant placement, and abutments were connected for submerged implant types D–F. Surgical conditions were the same as described above. First, the surgical sites were disinfected and the local anesthesia given. Over the top of these implants, a midcrestal incision was used combined with a small vertical relieving incision at the buccal and lingual aspect. Implants were uncovered after the elevation of a full-thickness flap. In the case of implants partially covered with bone (mostly in type F implants) a minor osteotomy was performed using hand instruments (chisel, mallet). Hermann et al . Biologic Width around oneand two-piece titanium implants This osteotomy likely had little effect on the outcome as the bone was quite thin, as evidenced by no changes during the submerged healing phase as shown in an earlier study of these implants (Hermann et al. 1997). Consequently, flat-head cover screws could be removed in the submerged implant group. Abutments of individual lengths were connected specific for each implant type so that after abutment connection all implants emerged to the same level. Interrupted sutures combined with a small V-shaped gingivectomy were used for wound closure around the abutments. Postoperative care and suture removals were done the same way as after extraction. Abutments on type C–F implants were loosened and immediately tightened afterwards at four, eight, and ten weeks after second-stage surgery to imitate the placement of another healing abutment, impression taking, as well as the placement of the final prosthetic component. Surgeries – Sacrifice All dogs were sacrificed three months after abutment connection of the submerged implants (Fig. 2). Euthanasia was carried out with an overdose of Euthanasia-5A Solution i.v. (pentobarbital sodium 0.2 mlΩ65 mg/kg bw. – Henry Schein Inc., Port Washington, NY, USA). Mandibles were block-resected with an oscillating autopsy saw (Stryker Co., Kalamazoo, MI, USA). The recovered segments with the implants were immersed in a solution of formaldehyde 4% combined with CaCI2 1% for histologic preparation and analysis. Nondecalcified histologic analysis – preparation Each implant with surrounding tissues was prepared for nondecalcified histology (Schenk et al. 1984). Specimens were carefully dehydrated and embedded in methyl methacrylate. Per implant, first one well-centered mesio-distal section was cut with a diamond saw (Vari/ Cut VC-50A, Leco Corporation, St. Joseph, MI, USA). The two remaining blocks were then glued together with an interposed plastic spacer (cyanoacrylate; MiocollA, Migros Company, Zürich, Switzerland), and subsequently sectioned in an oro-facial direction, resulting in up to five oro-facial sections. All sec562 | Clin. Oral Impl. Res. 12, 2001 / 559–571 tions were ground to a final thickness of approximately 80 mm and superficially stained with toluidine blue and basic fuchsin (Figs 4a–9b). Nondecalcified histologic analysis – histometry Histometric quantification was carried out using a light microscope (Vanox-TA, Olympus, Tokyo, Japan) at different magnifications (¿40–¿200) to best locate anatomical reference points. The microscope was connected to a high-resolution video camera (CCD-IrisA Color Video Camera, Sony Corp., Fujisawa, Japan) and interfaced to a monitor (MultisyncA XV17π, NEC, Itasca, IL, USA) as well as a personal computer (Vectra VLA, Hewlett Packard, Palo Alto, CA, USA). This optical system was associated with a digitizing pad and a bone histometry software package with image capturing capabilities (Image-Pro PlusA, Media Cybernetics, Silver Spring, MD, USA). Finally, the following measurements/calculations were performed at each implant site (Fig. 3): 1. Distance between the gingival margin (GM) and the most coronal point of the junctional epithelium (cJE)Ωsulcus depth (SD) 2. Distance between cJE and the most apical point of the junctional epithelium (aJE)Ωjunctional epithelium (JE) Fig. 3. Composite schematic (not true to scale) of histometric evaluation with the following measurements/calculations: Distance between the gingival margin (GM) and the most coronal point of the junctional epithelium (cJE)Ωsulcus depth (SD). Distance between cJE and the most apical point of the junctional epithelium (aJE)Ω junctional epithelium (JE). Distance between aJE and the first bone-to-implant contact (fBIC)Ω connective tissue contact (CTC). SD π JE π CTCΩBiologic Width (BW). Distances between the top of the implant (Top) and the GM, cJE, aJE, rough/smooth border (r/s), and the fBIC. Fig. 4. a. Mesio-distal section (overview) of a type A implant (one-piece, nonsubmerged). Nondecalcified histologic section; toluidine blue and basic fuchsin stain; original magnification ¿2.5; original inner/outer implant diameterΩ3.5 mm/ 4.1 mm; black barΩ1 mm. b. Close-up view of Fig. 4a. Left (distal) aspect of type A implant (onepiece, nonsubmerged). Note mild signs of periimplant inflammation. The white bar indicates the level of the first bone-to-implant contact (fBIC), the white arrow the most apical cell of the junctional epithelium (aJE), and the black arrow the top of the implant (Top). Nondecalcified histologic section; toluidine blue and basic fuchsin stain; original magnification¿8; black barΩ0.5 mm. Hermann et al . Biologic Width around oneand two-piece titanium implants Fig. 5. a. Mesio-distal section (overview) of a type B implant (one-piece, nonsubmerged). Nondecalcified histologic section; toluidine blue and basic fuchsin stain; original magnification ¿2.5; original inner/outer implant diameterΩ3.5 mm/ 4.1 mm; black barΩ1 mm. b. Close-up view of Fig. 5a. Left (mesial) aspect of type B implant (onepiece, nonsubmerged). Note mild signs of periimplant inflammation. The white bar shows the level of the first bone-to-implant contact (fBIC), the white arrow the most apical cell of the junctional epithelium (aJE), and the black arrow the top of the implant (Top). Nondecalcified histologic section; toluidine blue and basic fuchsin stain; original magnification¿8; black barΩ0.5 mm. 563 | Clin. Oral Impl. Res. 12, 2001 / 559–571 Fig. 6. a. Mesio-distal section (overview) of a type C implant (two-piece, nonsubmerged). Nondecalcified histologic section; toluidine blue and basic fuchsin stain; original magnification ¿2.5; original inner/outer implant diameterΩ3.5 mm/ 4.1 mm; black barΩ1 mm. b. Close-up view of Fig. 6a. Left (distal) aspect of type C implant (twopiece, nonsubmerged). Note moderate to severe signs of periimplant inflammation. The white bar delineates the level of the first bone-to-implant contact (fBIC), the white arrow the most apical cell of the junctional epithelium (aJE), and the black arrow the microgap (interface). Note that the abutment is not visible due to proper histological processing. Nondecalcified histologic section; toluidine blue and basic fuchsin stain; original magnification¿8; black barΩ0.5 mm. 3. Distance between aJE and the first bone-to-implant contact (fBIC)Ωconnective tissue contact (CTC) 4. SD π JE π CTCΩBiologic Width (BW) 5. – 9. Distances between the top of the implant (Top) and the GM, cJE, aJE, the rough/smooth border (r/s), and the fBIC. Statistical analysis The two principal soft tissue measures of interest for this study were the determination of the Biologic Width dimensions (Fig. 3) and the location of the gingival margin in relation to the implant. Each implant had one to three mesio-distal and up to five oro-facial sections yielding a total of 566 sites for histometric examination. In order to verify that the soft tissue values obtained from the histometric evaluation were not influenced by examiner bias, the primary examiner obtained two measures, as did a second examiner, for a subsample of 51 sites taken from six implants. The results of the comparison of the four readings of BW measures indicated the histometric evaluation was highly calibrated, with the four readings differing by less than 0.20 mm for 46 (90.2%) of 51 sites, with a maximum difference of 0.42 mm. Data were unavailable for 22.4% of sites (including all sites of one type C and one type E implant) that were unreadable due to histological processing (16.8%) or the degree of periimplant inflammation (5.6%). Also, the first boneto-implant contact (fBIC) for buccal sites tended to be lower than that for the corresponding lingual, mesial, or distal sites obtained from an implant. Biologic Width measures for nonbuccal sites within an implant generally ranged within 0.5 mm, but buccal sites tended to have distances 0.5 to 1.0 mm larger than any of the nonbuccal sites obtained from the same implant. Consequently, buccal sites tended to have BW values that were extreme outliers relative to the overall distribution of BW values for sites within an implant. These results indicated that only lingual, mesial, and distal sites should be used in this study to calculate mean values of the Biologic Width for each implant. For the purposes of consistency, buccal sites were also excluded in the calculation of mean values for each implant of all soft tissue measHermann et al . Biologic Width around oneand two-piece titanium implants urements. The remaining four to six sites per implant provided a sample sufficient to develop precise individual implant measures after averaging. A mixed-model Analysis of Variance was performed for each soft tissue measurement to check if implant types differed in a consistent fashion for each dog. If the resulting F-test was significant (P!0.05), then Bonferroni-corrected pairwise comparisons were made to identify implant type differences. Also, separate mixed-model ANOVAs were performed to ensure that position on the arch and side of the mandible did not influence the implant type results.