668 chapter 30 · a facial ridge lap crown, which does not allow proper hygiene or probing and...

668 IMPLANT SURGERY

Chapter 30

Posterior Single-Tooth Replacement:Surgical Guidelines

Carl E. Misch

Seventy percent of the dentate U.S. population is missing at least one tooth. Compared with past generations, single-tooth replacement will most likely comprise a larger percentage of prosthetic dentistry in the future. In 1960 the average American older than age 55 had just seven original teeth. Today the average 65 year old has 18 teeth, whereas the baby boomers can expect to have at least 24 teeth left when they reach age 65. Currently the fi rst teeth lost are usually between the ages of 35 and 54 years. Almost 30% of the 50 to 59 year olds examined in a U.S. national survey exhibited either single or multiple posterior edentulous spaces bordered by natural teeth.1 Treatment to replace single teeth in the posterior regions represents nearly 7% of the annual dental care reimburse-ment from insurance companies, and total estimated treatment costs for all patients missing a posterior tooth approximate $10 billion U.S. each year.2,3

POSTERIOR MISSING TOOTH

The fi rst molars are the fi rst permanent teeth to erupt in the mouth and are often the fi rst to decay. The adult patient typically has had one or more crowns fabricated to restore the integrity of the tooth and replace previous large restorations. Longevity reports of crowns have yielded very disparate results, with the mean life span at failure reported to be 10.3 years. The primary cause of failure of the crown is endodontic therapy, porcelain or tooth fracture, or uncemented restoration, which leads to decay. The posterior tooth is at risk for extraction as a result of these complications.1-9 Replacement of the posterior tooth is frequently necessary, and at least one of the adjacent natural teeth are virgin or minimally restored more than 80% of the time. Therefore, a traditional three-unit fi xed partial denture to replace a single tooth would remove the enamel on a completely healthy tooth and begin a cascade of potential complications, which often leads to loss of the tooth.

SINGLE-TOOTH IMPLANTS

From 1993 to the present, single-tooth implants have become the most predictable method of tooth replace-ment and therefore the treatment of choice. There are more refereed reports in the literature than for any other tooth replacement method. Becker et al. reported a more than 90% success rate in a study over 4 years of 282 molar implants.10,11 Simon et al. followed 70 molar implants over a period ranging from 6 months to 10 years with a 97.1% success rate.12 Levin et al. reported in 2006 on single-molar replacement with implants from 6 to 125 months (>10 years) with a 93.6% success rate.13

A 10-year report by Priest indicated the posterior single tooth was more than 97% successful.3 More important, there were no adjacent teeth lost from endo-dontic failure or causes, and only one tooth required endodontic therapy after implant insertion. This report clearly identifi es the adjacent teeth to be least at risk when the missing tooth is replaced with an implant. In a 2007 study, Misch et al. reported a 99% survival rate (11 initial healing failures and three late failures) for 1377 posterior single-tooth implants for as long as 10 years.14 A review of the literature by Goodacre et al. from 1981 to 2003 found single-tooth replacement with an implant had the highest implant prosthesis survival rate and averaged 97% survival.15 The most common complication reported was abutment screw loosening, which did not cause the prosthesis or implant to fail. In a consensus statement, Salinas et al. reported pooled success for single-tooth restorations exceeded the success rate of traditional fi xed partial dentures.16

IMPLANT BODY SELECTION

The implant body for a posterior single-tooth implant should include specifi c features to reduce complications. The most common problem associated with a single

668

Posterior Single-Tooth Replacement: Surgical Guidelines 669

tooth is abutment screw loosening.10,11,15,16 The higher the torque used to tighten the screw, the less the risk of loosening. Crest module and abutment connection designs, which decrease forces to the abutment screw, are also indicated. The implant must have an antirotational feature (e.g., an external or internal hex). The greater its height or depth, the less force transmitted to the abutment screw. However, the diameter of the implant is more signifi cant to reduce the stress. Accuracy of component fi t, the abutment screw design, and number of threads on the fi xation screw are other critical features.

The implant body should be made of titanium alloy to reduce the risk of long-term fracture, as it is four times more resistant to fracture than grade 1 titanium and twice as strong as grade 3 titanium. Sullivan reported a 14% implant fracture rate for single molars fabricated on standard-diameter Nobel Biocare implants (grade 1 titanium) and concluded that this is not a viable treatment.17 A threaded implant provides greater func-tional surface area than a cylinder, and a tapered implant provides less surface area than a parallel-walled implant body. When implant bodies are internal hex designs, the dimension of the implant in the posterior regions should be at least 4 mm or more in diameter to increase the outer body wall thickness and reduce the risk of long-term body fracture.

The ideal diameter of a single-tooth implant is depen-dent upon the mesiodistal dimension of the missing tooth and the buccolingual dimension of the implant site. When the facial bone thickness is inferior to 1.4 mm, bone loss may result and implant failures may occur with greater frequency.18 Horizontal bone loss around the implant causes increased probing depths or increased risk of soft tissue shrinkage. These may affect the bacterial fl ora or cervical esthetics of the soft tissue drape. This may be why gingival recession around wide-diameter implants has been noted to be greater than with a standard diameter.19,20 The ideal implant size is 1.5 to 2 mm from an adjacent tooth and has at least 0.5 mm of bone on the lateral aspects of the implant body. The ideal implant diameter in the intra-tooth posterior region should be at least 3 mm less than the mesiodistal dimension of the missing tooth (from cement-enamel junction [CEJ] to CEJ) and 3 mm narrower than the buccolingual dimension of bone. As a general rule, the molar implant should be larger in diameter than a premolar implant.

PREMOLAR IMPLANT REPLACEMENT

The most ideal posterior tooth to replace with an implant is the fi rst premolar, in either arch. The vertical available bone usually is greater than any other posterior tooth positions. In the maxilla, it is almost always anterior or below the maxillary sinus, and the mandibular fi rst premolar is almost always anterior to the mental

foramen and mandibular neurovascular complex. The bone trajectory for implant insertion is more favorable in the mandibular fi rst premolar than for any other tooth in the arch.

The maxillary premolars are often in the esthetic zone of patients with a high smile line. The need for bone grafting before maxillary fi rst premolar implant placement is very common, as the thin buccal facial plate is often lost during the extraction process. Implant placement without bone grafting may result in a recessed emergence profi le that, in the past, was corrected with a facial ridge lap crown, which does not allow proper hygiene or probing and should be avoided. To ensure proper esthetics and avoid the need for a ridge lap, the implant body often is positioned under the buccal cusp to improve the cervical emergence profi le of the maxillary premolar crown.

The natural premolar tooth root is 4.2 mm in diameter on average at a distance of 2 mm below the CEJ. As a consequence, the most common implant diameter is about 4 mm at the crest module. This also provides appro xi mately 1.5 mm of bone on the proximal surfaces adjacent to the natural teeth when the mesiodistal space is 7 mm or greater. However, when the mesiodistal dimen-sion is only 6.5 mm, a 3.5-mm implant is suggested.

The maxillary canine root is often angled 11 degrees distally and presents a distal curve 32% of the time, which may extend over the shorter root of the maxillary fi rst premolar. The mandibular canine also may have a distal inclination. The implant body is often longer than the natural tooth root of a premolar tooth. The surgeon may inadvertently place the implant parallel to the second premolar and, consequently, into the natural canine root. This may not only result in endodontic therapy of the canine, but also may cause root fracture and loss of the tooth (Figure 30-1, A). Therefore in the fi rst premolar region, care is taken to evaluate the canine angulation. The fi rst premolar implant may need to be placed parallel to the canine root and may need a shorter-than-ideal implant. A tapered implant body at the apical one third also may be of benefi t, to further decrease the risk of inadvertently engaging the canine root (Figure 30-1, B).

The second premolar apex may be located over the mandibular neurovascular canal or maxillary sinus. This results in a reduced bone height compared with the anterior region of the jaws and a shorter implant.

MOLAR IMPLANT REPLACEMENT

The molar mesiodistal dimension usually ranges from 8 to 12 mm, depending on the original tooth size and the amount of mesial drift of the second molar before implant placement. When one 4-mm-diameter implant is placed to support a crown with a mesiodistal dimension of 12 mm, this may create a 4- to 5-mm cantilever on the

670 IMPLANT SURGERY

marginal ridges. The magnifi ed occlusal forces (especially important in parafunction) may cause abutment screw loosening, an exaggerated emergence profi le on the crown, bone loss, and implant body fracture (Figure 30-2).

The most common complication of one regular 4-mm- diameter implant to replace a molar is abutment screw loosening. When the mesiodistal dimension permits, two 3.5- to 4-mm-diameter implants should be considered to restore the region to improve stress reduction and, in turn, reduce the incidence of abutment screw loosening. In a 3-year report of posterior fi rst-molar replacements, Balshi et al.21,22 found implant screw loosening was a common complication when one implant replaced the tooth (48%) and was reduced to 8% when two splinted implants replaced the fi rst molar. Other studies found the one-wide dia meter implant had greater screw loosening

than two splinted implants.23,24 A 50% decrease in mesiodistal and buccolingual stress was found between a 5-mm and two splinted, standard-diameter implants.24

Therefore, whenever possible, two splinted implants should be used to replace a larger single-molar space.

As mentioned earlier, Sullivan reported a 14% implant fracture rate for single molars on a standard, 4.1-mm implant.17 Rangert et al. reported overload-induced bone resorption appeared to precede implant fracture in a signifi cant number of single-molar implants, which were 4 mm in diameter.25

When the mesiodistal dimension of the missing tooth is 8 to 12 mm with a buccolingual width greater than 7 mm, a 5- to 6-mm-diameter implant body is suggested to reduce the stress to the implant system. Langer et al.26 also recommended the use of wide-diameter implants in bone of poor quality or for the immediate replacement of failed implants. The larger- diameter implant does not require as long an implant, which also is a benefi t because of the reduced posterior vertical bone height due to anatomical limitations. When possible, a larger diameter implant (or two splinted, traditional-size implants) should be inserted to enhance the mechanical properties of the implant system through increased surface area, stronger resistance to component fracture, increased abutment stability, and enhanced emergence profi le for the crown.

When the posterior space is 14 mm or greater, the largest implant diameter for two adjacent implants may be calculated by subtracting 6 mm (1.5 mm from each tooth and 3 mm between the implants) from the intratooth distance and dividing by 2 (Figure 30-3).

16 mm – 6 mm2

= 5 mm for each implant.

A BFigure 30-1 A, A maxillary canine root is often slanted 11 degrees distally and has a distal curvature 32% of the time. When the implant is placed parallel to the fi rst premolar, it may inadvertently encroach upon the canine root. B, A maxillary fi rst premolar implant may need to be parallel to the canine.

Figure 30-2 When a mesiodistal space is 14 mm, standard 4- mm-diameter implants will have a 5-mm cantilever, which increases the force to the cement, abutment screw, marginal bone, and implant body. Therefore an increased risk for biomechanical complications occurs.


It should be noted the diameter used is the crest module dimension, which is often 0.2 to 0.35 mm greater than the implant body dimension (i.e., 4.1/3.75 mm for Nobel Biocare SteriOss, 3-I, LifeCore). The two implants should be 3 mm apart, because the width of the crestal defect around an implant is usually less than 1.5 mm. The two adjacent implants 3 mm or more apart will not convert the angular defect next to each implant into a horizontal defect, which may increase sulcus depths or cause a loss of papilla height.27 When possible, two regular-size or one regular and one large-diameter implant are suggested when replacing molars. The space is usually restored with two premolar-size crowns, rather than a large molar with a furcation (Figure 30-4).

When the posterior mesiodistal space between teeth is 12 to 14 mm, the treatment plan of choice is less obvious. A 5-mm-diameter implant may result in canti -levers up to 5 mm on each marginal ridge of the crown. However, two implants present a greater surgical, pros-thetic, and hygiene risk. The fi rst option is to slightly reduce the standard implant diameter to 3.5 mm, rather than 3.75 or 4.0 mm. The primary space requirement is reduced to 13 mm of space, instead of 14 mm. Additional space also may be gained in several ways:

1. Enamoplasty of the adjacent teeth proximal contours to increase the mesiodistal dimension of the missing tooth. It is not unusual that the distal natural tooth has tipped toward the edentulous space. An enamoplasty may be even more effective in these cases to increase space (Figure 30-5).

2. Orthodontics to upright a tilted second molar or increase the intratooth space. One anterior implant

8-12 mm

5

A

14 mm

1.5 mm 1.5 mm

3 mm

44

B

Figure 30-3 When the intratooth space is 14 mm, the ideal implant size is 14 mm – 6 mm (1.3 mm from each tooth and 3 mm between the implants) ÷ 2 = 4 mm for each implant.

A

BFigure 30-4 A, When the intratooth space is 14 to 20 mm, two implants are used to restore the space. The implants are positioned 1.5 to 2.0 mm from each tooth. B, The two implant crowns to restore a space 14 to 20 mm are splinted together and usually made the size of premolars.

672 IMPLANT SURGERY

may be placed and an orthodontic spring incorporated in the transitional crown. The spring pushes the distal tooth more distal and, after orthodontic movement, the second implant may be inserted with less risk and improved hygiene between each implant. Another option is to reduce the space orthodontically and place only one implant and crown.

3. The implants may be offset with one implant placed buccal and the other implant on a diagonal toward the lingual28 (Figure 30-6, A). The diagonal dimension increases the mesiodistal space by 0.5 to 1 mm. In the mandible, the most anterior implant is placed to the lingual aspect of the midcrest and the more distal implant is placed to the facial aspect to facilitate access of a fl oss threader from the vestibule into the intraimplant space. The occlusal contacts also are slightly modifi ed on the buccal aspect of the mesial implant to occlude over the central fossa (Figure 30-6, B). In the maxilla, the anterior implant is placed facially and the distal implant palatally to improve

esthetics. The distal occlusal contact is placed over the lingual cusp and the mesial occlusal contact is located in the central fossa position. The cervical esthetics of the maxillary molar are compromised on the distal half of the tooth to the benefi t of greater intratooth distance and easier access for home care. This maxillary implant placement requires the intraimplant furcation to be approached from the palate, rather than the buccal approach, as the mandible.

POSTERIOR SINGLE-TOOTH IMPLANT SURGERY

The ideal location to begin a surgical experience in implant dentistry is a posterior single tooth, out of the esthetic zone, and in abundant bone volume. Surgical success rates for single-tooth implants are often more than 98%. University reports show predoctoral students

A

B C

12-14mm(increase to 14mm)

Ø4 Ø4

Figure 30-5 A, When 12 to 14 mm of space is available, the mesial and distal contour of the adjacent teeth is modifi ed to gain addition space. B, A periapical radiograph of two 3.7-mm implants to replace one molar, in which the proximal contours of adjacent teeth were reduced. C, An intraoral view of the mandibular fi rst molar, replaced by two 3.7-mm implants (BioHorizons Maestro Dental Implants).


have achieved excellent results in these conditions.28-31 For example, Bell et al. reported no failure in 120 implants during a 4-year period with selected predoctoral dental students.28 Cummings et al. found senior pre doctoral dental students had no implant failures of 71 implants during 5 years.29

Posterior single-tooth implants may be technically easier and have less risk than performing an endodontic treatment on a tooth with a single canal. Rather than working on a diseased pulp with different local condi-tions, an implant surgery is in healthy bone and an ideal clinical situation. In endodontics, the fi les and obturation should be within 0.5 mm of a tooth apex. Implants may be prepared and inserted 0.5 to 10 mm from an opposing landmark. Endodontics requires the removal of necrotic debris from an oblong canal, with lateral canals and root curvatures or dilacerations. An implant osteotomy is round in diameter and made with round-diameter drills and always a straight channel. Endodontics requires obturation with a plastic material,

able to fi ll irregular-diameter and shaped canals. Underfi lls may result in failure of the procedure. Implant round-diameter osteotomies are obturated with a round-diameter implant precisely fabricated for the size of the osteotomy. Underfi lls of the osteotomy will fi ll in with bone next to the implant, with no clinical consequence. An implant surgery may be completely aborted at almost any time, and several months later the bone conditions are healed and similar to the original bone site conditions.

SURGICAL PROCEDURE

There are three approaches for posterior single-tooth implant surgery: (1) two-stage surgery, (2) one-stage surgery, and (3) direct, one-stage surgery (Table 30-1).

Two-Stage Surgery

In an early learning curve, the two-stage surgical approach offers several advantages. This method provides direct vision of the crestal bone width and length. The direct observation of crestal bone ensures adequate width of bone is available for implant placement. The width of bone is often reduced after initial socket healing. If

4

4

B L

B L

44

A

BFigure 30-6 A, When the mesiodistal space is 12 to 14 mm, the implants may be offset to increase space between the implants. In the mandible (left) the distal implant is positioned more buccal and the mesial implant more lingual. In the maxilla, the mesial implant is more buccal and the distal implant is more lingual. B, An intraoral view of a mandibular fi rst molar with offset implants. The distal implant is more buccal, which facilitates fl oss threader insertion for oral hygiene.

Table 30-1 Comparison Between Two-Stage, One-Stage, and Direct One-Stage Surgeries

TWO- ONE- DIRECTTOPIC STAGE STAGE ONE-STAGEBone anatomy Yes Yes No

visual controlOsteotomy Yes Yes No

visual controlCover screw/ Below Above Above

PME tissue tissue tissueBone graft Yes Maybe NoExposure to No Yes Yes

intraoral bacteria

Surgical 2 1 1appointments

Prosthetic At or At or Above tissueconnection/ below aboveimplant tissue tissueplatform level More Easier Easier diffi cult

Reposition Yes Yes Nokeratinized facially

Transitional Yes Yes-No Yes-Noappliance

Stage II Yes No Noneeded

PME, Permucosal healing extension.

674 IMPLANT SURGERY

inadequate, a bone graft should be performed before implant insertion. In more experienced situations, the implant may be inserted at the same appointment as the bone graft. The implant is inserted at or slightly below the crest of bone in this technique. A low-profi le cover screw is then inserted into the implant body. The tissues are then approximated over the implant for primary closure. A removable transitional prosthesis may be delivered post surgery when in the esthetic zone and in the absence of a bone graft (Figure 30-7).

The advantages of this approach include: (1) direct observation of crestal bone volume before osteotomy; (2) direct observation during osteotomy preparation; (3) ability to bone graft the site at the time of implant placement; (4) implant body healing at or below the crest of bone, which reduces risk of early loading during initial bone healing; (5) local hygiene issues or anaerobic bacterial infi ltration are not critical factors during initial healing; and (6) the ability to deliver a soft tissue–borne transitional appliance in the esthetic zone.

The technique requires a second-stage surgery to uncover the implant body. The advantages of this procedure are the crestal and facial region may be directly evaluated and minor defects corrected before beginning the pros-thetic reconstruction. On occasion, soft tissue has invaded

the crestal zone of the implant, and a one-stage approach does not evaluate the region before restoration. The facial plate of bone may also resorb during initial healing and may be grafted at the reentry surgery.

One-Stage Surgery

A one-stage surgery uses a similar incision and refl ection technique to observe directly the crestal bone volume. However, at the conclusion of the implant surgery, a permucosal healing element (PME) is placed into the implant body. The implant body also is usually placed slightly above the crest of the bone. The soft tissue is then placed around the PME (Figure 30-8). The advantages of the one-stage surgery are:

1. The soft tissue matures while the bone interface is healing. This permits the restoration to be fabricated with complete assessment of the soft tissue profi le. In the two-step procedure, the soft tissue is less mature when the prosthesis is fabricated, as a stage II surgery is required to uncover the implant and place a PME or abutment.

2. A second surgical procedure and suture removal appointment are not necessary. This saves the patient

A B

C D EFigure 30-7 A, A two-stage surgery refl ects the soft tissue and directly observes the underlying bone. B, A single-tooth implant is threaded into the osteotomy (BioHorizons Internal Dental Implant) for a posterior single-tooth replacement. C, A low-profi le cover screw is inserted into the implant body. D, The fi rst-stage surgery uses primary closure over the implant site during initial bone healing. E, A periapical radiograph of the implant in position to replace a single molar.

Text continued on p.677.


A B

C D

E FFigure 30-8 A, The mesiodistal dimension of a missing tooth for a single-tooth implant should be at least 6.5 mm in the posterior region of the mouth (measured between the CEJs). This permits an implant at least 3.5 mm in diameter. B, A periapical radiograph is used to evaluate available bone height. It should be at least 11 mm from the crest to the opposing landmark (i.e., the mandibular foramen and mandibular canal). C, In the present case, a one-stage surgical approach may be selected instead of a direct one-stage approach to reposition the keratinized tissue facially. The soft tissues are refl ected for direct observation of the bone volume and dimension during the preparation of the implant osteotomy. D, A 2-mm-diameter, end-cutting starter drill is used initially under copious cooled sterile saline. E, A 2-mm-diameter, 9-mm-long force direction indicator with a 4-mm-diameter “stop” is placed in the osteotomy. F, A periapical radiograph is made of the force direction indicator (depth gauge). The adjacent roots are evaluated in relation to the device, and the distance from the opposing landmark is evaluated. Continued

676 IMPLANT SURGERY

G H

I J

K LFigure 30-8, cont’d G, The osteotomy is prepared according to the drill sequence indicated for the bone density specifi c to the site. H, A crestal side-cutting drill is used to prepare the crest module dimension of the implant. I, The implant is inserted into the osteotomy with a hand piece at reduced rpm. J, A postoperative radiograph is made when the implant is in its fi nal position. It is evaluated relative to depth and the opposing landmark, the adjacent tooth roots, and for crestal position. K, In a two-stage surgical approach, a low-profi le healing cap is threaded into the implant body (left). After hard and soft tissue healing, a higher-profi le permucosal extension (PME) is placed with a second surgery (right). A one-stage surgery places the PME (right side) at the initial surgery. The suture groove region decreases the risk of soft tissue growing over the PME during healing (BioHorizons Dental Implants). L, In a one-stage surgical approach, a PME is placed after the insertion of the implant. Continued


discomfort and the surgeon two appointments (stage II uncovery and suture removal).

3. The abutment to implant connection may be placed above the crest of bone in the one-stage surgery. This higher location of the implant-abutment connec tion may reduce some of the early crestal bone loss in a developing implant interface. In addition, Weber observed an improved hemidesmosome soft tissue–implant connection when the components above the bone were not removed and reinserted, as when the healing gap connection is below the bone.32 Depending upon crest module design, the one-stage surgical approach may have less early crestal bone loss.

4. The higher-profi le implant body also allows the restoring dentist to attach the prosthetic abutment with greater ease and tactile ability. Impression caps also may be inserted when the abutment connection is above the bone, which further simplifi es the restorative procedure (Table 30-1).

An advantage of the one-stage surgery, compared with a direct or fl apless one-stage approach, is the attached keratinized tissue may be repositioned to ensure an

adequate zone on the facial aspect of the PME and implant abutment. In addition, direct observation of the bony crest permits bone grafting and a precise implant crest module position relative to the crest because it can be directly observed. In theory:

1. The higher-profi le PME is more at risk of loading during healing, especially when an overlying soft tissue–borne transitional restoration is worn. Therefore a disadvantage may be a higher healing failure rate. However, clinical studies of one-stage surgery indicate similar implant survival rates in good bone volumes and quality.

2. The amount of keratinized tissue should be adequate to reposition at least 1.5 mm to the facial aspect of the PME healing cap.

3. When a bone graft is considered at the time of implant insertion, primary closure of the soft tissues improves the environment to grow bone. Therefore the one-stage approach is less indicated under these conditions.

4. The implant PME may be unesthetic when the maxil-lary esthetic zone of the mouth is in a premolar site.

M N

O PFigure 30-8, cont’d M, The tissue is sutured around the PME during the initial implant surgery for a one-stage surgical approach. N, After healing, the prosthesis fabrication may be started. No second-stage incision or tissue refl ection is needed in this case. O, Final prosthesis delivery. P, Periapical radiograph of fi nal restoration.

678 IMPLANT SURGERY

Direct (Flapless) One-Stage Surgery

The one-stage surgical approach may be modifi ed with a direct fl apless surgical approach. This technique does not refl ect the crestal soft tissue. Instead, a core of keratinized tissue (the size of the implant crest modale diameter) is removed over the crestal bone. The implant osteotomy is then performed in the center of the core of the exposed bone. This technique requires no sutures around the PME. The advantages of this technique are similar to a one-stage surgical approach. In addition, there is less soft tissue trauma because the tissues are not refl ected. As a result, discomfort, tenderness, and swelling are usually minimal (Figure 30-9).

The primary disadvantage of the direct approach is the inability to assess the bone volume before or during the implant osteotomy or insertion. Therefore this tech-nique should only be used when the bone width is abundant (>8 mm). Bone grafting needs and procedures cannot be precisely evaluated. The soft tissue around the implant site should be ideal in amount of attached keratinized mucosa, as the soft tissue pouch is over the bone site, not in a region related to the soft tissue. Often, the keratinized tissue is reduced on the buccal half of the ridge and the tissue punch may inadvertently remove all the keratinized tissue on the facial aspect of the implant. As the crest of the ridge is below the soft tissue, it is diffi cult to see lines on the drill to access the depth of drilling. Therefore stops on the drill are particularly benefi cial. The surgeon also has trouble assessing the location of the implant crest module in relation to the crest of bone because it is also below the soft tissue. In addition, the interdental papillae may not

be elevated with this technique. Therefore the soft tissue drape should be ideal in volume of keratinized tissue, both faciolingually and mesiodistally.

STEP-BY-STEP SURGERYImplant Site Evaluation

The missing tooth space is fi rst evaluated from a mesiodistal dimension, at the level of the CEJ of each adjacent tooth. This dimension should be at least 6.5 mm in width. The selected implant diameter is 3 mm narrower than this dimension (i.e., at least 3.5 mm). The bucco lingual crestal dimension is then evaluated with the soft tissue intact. The edentulous site should be at least 9 mm wide with the tissue intact to consider a direct (fl apless) one-stage surgery (assuming the tissue thickness in each site is 1 mm). When a smaller dimen-sion is present a one- or two-stage procedure is indicated and the ridge most often will require a bone graft, either before or in conjunction with implant insertion. If the facial aspect of the implant body is exposed at insertion, a two-stage approach is indicated, along with a membrane bone graft.

A periapical radiograph is then used to evaluate the missing tooth site. The minimum radiographic bone height should be 11 mm from the crest of the ridge to the opposing landmark (i.e., mental foramen and mandibular canal in the mandible and maxillary sinus in the maxilla). This dimension permits a 9-mm-long implant to be inserted at least 2 mm above the opposing landmark in the mandible. The roots of the adjacent teeth should not invade the vertical column of bone

A B CFigure 30-9 A, A direct one-stage surgery uses a fl apless approach. A core of soft tissue is removed over the implant site. The osteotomy is prepared in the center of the core. B, The implant is threaded into position. It is often diffi cult to determine the position of the implant in relation to the crest of the bone, as it is not directly visible below the soft tissue. C, A permucosal healing element (PME) is threaded into position and seals the soft tissue opening.


in the implant site. The 6.5-mm minimum mesiodistal dimension should exist for at least 11 mm between the adjacent roots. The minimum implant length selected is usually 9 mm, and the longest length is at least 2 mm less than the available bone height dimension in the mandible, closer in the maxilla, and may even proceed to the sinus fl oor.

Soft Tissue Refl ectionOnce the bone volume is assessed and the implant surgical option is identifi ed (i.e., two-stage, one stage, direct), the implant procedure may commence. In the one- or two-stage approach, the soft tissue refl ection is similar. A scalpel (#12 and/or #15) is used to incise the mid-crestal tissues. At least 1.5 mm of keratinized tissue should be left on the buccal to this incision line.

The incision line most often is extended through the interproximal and sulcular tissues of the adjacent teeth. This permits complete assessment of the crestal bone volume when the tissues are refl ected. A Buser or Molt elevator is used to make a full-thickness soft tissue refl ection and expose the crestal bone and a few millimeters of the lateral aspects of the implant site. The buccolingual dimension of bone is measured and confi rmed to be greater than 7 mm in width. If the site is less than 7 mm wide, a division B membrane and layered-approach bone graft are used to augment the site, either in conjunction with implant insertion or as a separate surgical procedure before placing the implant.

Implant OsteotomyA 2-mm-diameter, end-cutting starter drill is used in the mesiodistal and buccolingual centers of the crestal bone for implants in the mandible or out of the esthetic zone in the maxilla. The osteotomy is made with an electric motor at a preferred speed of 2500 rpm under copious amounts of chilled saline irrigant. The osteotomy is made 7 to 9 mm deep in the bone (Figure 30-10, A).

Once the initial osteotomy is prepared, it is assessed for proper position. If incorrect, the hole may be “stretched” to the proper location by a side-cutting Linderman bur (Figure 30-10, B). This bur makes the hole oblong toward the corrected center position. The following end-cutting drills may then be positioned into the correct position and create a round osteotomy of proper size before implant placement.

A 2-mm-diameter direction indicator (depth gauge) is then inserted into the osteotomy and the angulation and position assessed (Figure 30-10, C). When the “stop” on the direction indicator is the same size as the implant (i.e., 4-mm diameter), the fi nal implant position bucco-lingual and mesiodistal also may be assessed, making sure it is at least 1.5 mm from each tooth and 1.5 mm from the outer crestal cortical plates. If it is too far in any direction, a side-cutting Linderman drill may stretch the osteotomy toward a more proper position. A periapical

radiograph is made with this measuring tool. The radio-graph ensures the proper angulation and position of the implant relative to the adjacent tooth roots. The fi nal diameter of the implant may now be selected using the guidelines presented earlier. The opposing landmark is also evaluated. The implant is most often placed 2 mm or more from the mandibular neurovascular canal or 0.5 mm from the fl oor of the maxillary sinus and at least 9 mm in length. Although implants may be inserted closer than 2 mm of these landmarks without compromise, the 2-mm surgical rule is a common safe position in the mandible. When the opposing landmark is 14 to 17 mm farther away from the depth gauge and the osteotomy may be safely made deeper than 9 mm, the pilot 2-mm diameter drill may be reinserted into the osteotomy and prepared to a 12- or 15-mm length. Rarely is more than a 15-mm-long implant required.

When the opposing landmark is safely beyond the end of the osteotomy depth, the drills often proceed end-cutting 1 to 2 mm beyond the eventual depth of the implant. The slight recess area in the apical end of the osteotomy serves several purposes:

1. Bone debris may fi ll the region during a self-tapping implant body placement, because the threads scrape the bone as the implant is inserted. As a result, when the implant comes to its fi nal position, the bone debris does not impede its progress.

2. The implant may be rotated in fi nal position to align the fl at section of the antirotation crest module, which helps identify the position location of prosthetic components.

3. The lingual border of the osteotomy is often higher than the facial bone level. A stop used on a drill for the implant length prevents the drill from proceeding to the facial crest, and the crest module height will be determined by the higher lingual plate of bone, which positions the facial aspect of the implant platform above the bone.

A 2.5-mm-diameter, end-cutting twist drill is then used in the initial osteotomy to the depth established. The drill also rotates at 2500 rpm with copious amounts of chilled sterile saline. The osteotomy location and angulation are reassessed at this point. A slight correc-tion of position or angulation with a Linderman drill is possible with little consequence or risk. A 3-mm-diameter twist drill is then used (depending upon implant design and fi nal diameter) to the desired length, followed by a 3.4-mm twist drill. Once again, the proper location and angulation of the osteotomy is verifi ed (Figure 30-10, D, E, F, G). This is the fi nal diameter for a 4-mm-diameter implant (BioHorizons Dental Implants). The fi nal osteotomy diameter for a 4-mm-diameter implant is related to the implant diameter and manufacturer. For example, a Zimmer implant uses a 3.2-mm diameter for a 4- mm-diameter implant. Most implant drill kits clearly

680 IMPLANT SURGERY

identify the drill sequence and fi nal osteotomy diameter related to each diameter implant (Figure 30-10, H).

Most implant crest modules are larger in diameter than the implant body. The larger diameter often requires a side-cutting crest module drill in D1 or D2 crestal bone situations to prepare the crestal aspect of the implant osteotomy. This drill is not used when the bone density is poor (D3, D4) (Figure 30-10, I).

In dense bone types, some implant thread designs require a bone tap or thread former to prepare the threads in the bone before implant insertion (Figure 30-10, J).

When the bone is soft (D3 or D4) or implant thread design is shallow (e.g., 0.2 mm versus 0.5 mm), a thread former is not required. Most often for single-tooth implants, the thread formers or taps should use a high-torque, slow-speed handpiece and be rotated at less than 30 rpm into the bone. Irrigation is also of benefi t to help lubricate and clean the bone tap and osteotomy site of debris during this process.

The implant site may then be prepared for implant insertion. The osteotomy is lavaged and aspirated to remove bone debris and stagnant blood. This reduces

A B C

D E F

GFigure 30-10 A, The soft tissue is refl ected from the crest of the ridge and the width of bone is directly assessed. A 2-mm-diameter, end-cutting starter drill is used under copious sterile saline. B, A 2-mm-diameter, 9-mm-long force direction indicator is positioned into the initial osteotomy. C, A side-cutting Linderman drill is used to modify the initial osteotomy started with the pilot drill. D, A 2-mm-diameter pilot drill is inserted into the initial osteotomy and prepares the bone from 12 to 15 mm when the opposing landmark permits. A 2.5-mm, then a 3-mm drill sequence prepares the osteotomy. E, A 3-mm side-cutting twist drill widens the osteotomy. F, A 3.4-mm-diameter, end-cutting twist drill is used to prepare the fi nal diameter for a 4-mm implant body. G, An implant drill kit with color coding most often identifi es the drill sequence and the fi nal diameter related to each implant size (BioHorizons Maestro Dental Implants). Continued


the risk of these materials being forced into the bone marrow spaces or neurovascular channels during implant insertion, thus causing hydrostatic pressure. This pres-sure may increase the devital zone of bone around the implant or even cause short-term anesthesia when the implant site is in the vicinity of the mandibular canal.

The implant is rotated less than 30 rpm into position by a low-speed, high-torque hand piece or a hand ratchet (Figure 30-10, K). The implant should not require a torque greater than 35 N-cm while threading into position. If this is necessary, the implant should be unthreaded and a bone tap used before insertion. The implant is usually inserted slightly above (one stage) or below (two stage) the crest of the bone, depending upon a two-stage or one-stage surgical approach, as previously described. The implant should be rigid upon placement, with no observable mobility under slight compressive forces. The implant should not be tightened into the osteotomy, such as a nut onto a bolt. A torque value up to 35 N-cm is considered safe with most threaded implant designs. However, excessive pressure to the bone may cause pres-sure necrosis and increase the devital zone of bone around the implant during healing. When in doubt, the implant

may be unthreaded one half turn with a hand ratchet, to ensure it is not too tight within the osteotomy.

A postinsertion periapical radiograph is made once the implant is in fi nal position. The radiograph is eva-luated as to implant depth and the opposing landmark, the adjacent roots and the position of the crest module and the crest of the bone. Any correction is most easily made at this time, rather than attempting to modify the position at a later date.

It should be noted that the implant surgery may be aborted at any stage of the procedure. Unlike a crown preparation or endodontic therapy, an aborted procedure will allow the bone to reform in the osteotomy and allow the procedure to be performed with a similar condition as the initial surgery at a later date. Therefore if the implant position is not within the range of ideal, it may be removed, and a new implant reinserted several months later in a more ideal position.

The abutment mount of the implant body is then removed. When a two-stage implant insertion is used, a low-profi le cover screw is inserted into the implant body (Figure 30-10, L, M). When the cover screw is in fi nal position, it may be slightly tightened, loosened, and

H I J

K L MFigure 30-10, cont’d H, A side-cutting crestal bone drill prepares the top of the implant osteotomy in D1 and D2 bone, as the crest module of the implant is larger than the implant body. I, A bone tap is used in denser bone to prepare thread forms before implant insertion. J, A slow-speed, high-torque hand piece is usually used to thread the implant into the bone at 30 rpm or less. K, The abutment/mount of the implant body is removed once the implant is in fi nal position. A low-profi le cover screw is inserted for a two-stage surgical approach. L, A permucosal extension (PME) is inserted into the implant body for a one-stage surgical approach, which is used most often in the posterior region of the mouth. M, The most common, undisturbed healing time for a single-tooth implant is 4 months. At this point, both the hard and soft tissues are adequately healed and the fi nal restoration may commence.

682 IMPLANT SURGERY

tightened again. The implant should not rotate during this procedure. A similar procedure is performed with a PME, when a one-stage or direct surgical approach is used. In the posterior of the mouth, a one-stage surgical approach is used most often.

In a one- or two-stage surgery, two interrupted sutures approximate the soft tissue for primary closure. Most often a 4-0 polyglycolic acid (PGA) material is used. Slight pressure to the approximated tissues for 4 to 6 minutes decreases bleeding and improves the adaptation of the tissue to the bone and PME. When not in the esthetic zone, no transitional device is worn. Postoperative instructions include the use of periodic ice to the region for 3 days, and postoperative medication is similar to a routine extraction. The sutures are removed after 10 to 14 days, although 7 days are usually suffi cient. The most common undisturbed healing time for a single-tooth implant before restoration is 4 months. At this point, the hard and soft tissues are adequately healed and the fi nal restoration may commence (Figure 30-10, N).

In the past, the most common choice to replace a missing posterior tooth was a three-unit fi xed partial denture. The choice of not replacing the tooth is a more frequent option for mandibular second molars, but this option also may be selected when the intratooth space is small and the occlusion prevents migration. Today, with the improvements in implant materials, design, surgical approach, and prosthetic guidelines, and with reported success rates greater than 97%, the use of implants to replace a single tooth is often the treatment of choice. Improved hygiene, less risk of decay of the adjacent teeth, less endodontic risk, less risk of adjacent tooth loss, maintenance of bone, and prosthesis longevity all favor an implant restoration compared with the three-unit fi xed partial denture prosthesis.

Posterior single-tooth implant surgery in abundant bone is one of the easier processes in implant surgery. It is often easier than performing endodontics for a single rooted tooth. Early learning curves are short, and very high surgical success rates are rapidly obtained. The guidelines within the chapter for implant body size (width and length) have proven that predictable long-term surgical success for single-tooth implants is more than 99%.

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668 chapter 30 · a facial ridge lap crown, which does not allow proper hygiene or probing and...

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