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Written by Gary Greenstein, DDS, MS, John S. Cavallaro, Jr, DDS, and Dennis P. Tarnow, DDS Saturday, 01 May 2010 00:00
There is a large body of evidence that supports the success of dental implants. The dental literature also contains many clinical procedures that were developed to facilitate implant placement. In addition, clinicians have contributed, via discussion or lecture, ideas and techniques to manage diverse situations. Many of these concepts that can make clinical practice easier are not universally known, and others have not been published.
This article was written to gather and share information referred to as “clinical pearls” that can enhance planning, placement, and monitoring of dental implants. Numerous topics are addressed and no attempt is made to cover subjects in detail. Instead, within a limited discussion pertaining to various issues, specific clinical suggestions or facts are provided that may improve clinical outcomes. The following topics will be discussed in this 4-part article: diagnostic procedures, insertion of implants, adjunctive implant procedures, and handling postoperative complications.
|Figure 1. The correct probing force is 25 gm. This force when applied with a probe causes blanching of the nail bed.|
Diagnostic probing should be done with a 25-gm force (the pressure it takes to blanch a nail bed with a probe) (Figure 1).1 Deeper than usual probing depths around an implant may not reflect peri-implantitis, since an implant that is placed subgingivally can result in a deep sulcus.2
Contributing to this finding is the fact that connective fibers adhere to, but are not attached to, an implant as they are to teeth. Therefore, they do not impede probe tip penetration. Nevertheless, it is valuable to monitor probing depths after insertion of an implant, because subsequent changes in measurements may reflect disease progression. Relative attachment levels also can be recorded using a fixed reference point on the restoration (eg, measurement from crown margin to base of the pocket). Probing assessments do not adversely affect the epithelial attachment to an implant, because the junctional epithelium usually heals within 7 days.3 Furthermore, probing assessments can help avoid frequent x-rays to detect alterations in bone levels.
Radiographs are the best way to assess support around implants and ought to be obtained every 24 to 36 months for routine monitoring.4 They should be taken more frequently if probing or attachment level alterations are detected, or if swelling or pain exists.
X-Ray Interpretations—Several radiographic findings of diagnostic and clinical interest are addressed. Clear depiction of implant threads on an x-ray reflects good radiographic angulation. When threads are clear on one side of the implant and not apparent on the other side, the radiographic angle is incorrect by 10º; if both sides are unclear, the film is undiagnostic.5 A perpendicular orientation of the radiographic beam is important when assessing the connection between an implant and an abutment. If the angulation of an x-ray is inaccurate by more than 10º, superior-inferiorly, implant parts may appear mated when they are separated. In this regard, bite-wings provide greater diagnostic accuracy than periapical films.
Figure 2. Thick radiopaque crest reflects ridge resorption.
Figure 3. Endodontic Rinn holder used with guide pin.
Periapical Films of Direction Indicators—When guide pins are inserted into an osteotomy in an edentulous area, it is not possible for a patient to bite down on a regular bite tab or Rinn holder. A special Rinn holder employed for endodontic instruments can be used to take a radiograph with a direction indicator in place (Figure 3).6 Another method for radiographic assessments involves shortening guide pins or purchasing ones that are reduced in size (Gelb radiographic depth gauge),7 so that they could be used with a standard Rinn holder. If no radiographic aids are available, a regular direction indicator can be inserted into the osteotomy and a hemostat should be utilized to position the film. Place the hemostat horizontally across the inferior border of the film, and have the patient hold the hemostat during the x-ray exposure.
|Table. Distortion on Radiographs|
Accounting for Radiographic Distortion—Table lists mean linear radiographic errors with respect to different x-ray techniques when locating the mandibular canal.8 The numbers in the table represent mean errors, and they can be incorrect by even larger amounts. These inaccuracies need to be taken into account when creating an osteotomy in sensitive areas. For example, if a sinus elevation is planned and the periapical film indicates there is 5 mm of bone subantrally, do not drill to 4 mm, because if there is a 20% radiographic error, the twist drill can penetrate the sinus, and the ability to elevate the Schneiderian membrane will be compromised. Go a little shorter and verify the drill’s position with a periapical film. To avoid misinterpretation of linear measurements on radiographs, clinicians can use markers of known dimension when taking an x-ray (eg, 5 mm diameter ball bearing) or obtain a computed tomography (CT) scan for more accurate measurements.
Detecting the Inferior Alveolar Nerve
Figure 4. Inferior alveolar nerve next to apex of a tooth. Usually it is several millimeters away from the apex of the mandibular first and second molars.
Prior to developing an osteotomy over the inferior alveolar nerve, its position must be detected radiographically. A combination of periapical and panoramic film should provide a good estimate of the nerve canal’s apicocoronal position. On average, the distance from the apex of the mandibular first and second molars to the inferior alveolar nerve varies from 3.5 mm to 5.4 mm.9 However, the nerve’s position can fluctuate from being many millimeters away from the apex of a mandibular first molar to being adjacent to it (Figure 4). If the nerve’s position is not clear, then a CT scan should be ordered. Similarly, if the mandibular canal is 10 mm or less from alveolar crest, consider ordering a CT scan. A good general rule to follow dictates that if you are wondering if you need a CT scan, then order one. Without a clear depiction of the nerve’s position before initiating an osteotomy, clinicians are at risk of causing a parasthesia.
Determining Thickness of the Alveolar Ridge Without a CT Scan
Radiographs provide 2-dimensional assessments that can be used to assess bone height in the maxilla and mandible. However, without a CT scan, clinical determinations of bone width can be misleading. To determine alveolar bone width in the maxilla or mandible, a caliper (eg, Vernier) can be employed to map the width of the ridge (combined soft tissue and bone thickness) at the crest and then every 3 mm up to the vestibule.10 After local anesthesia, the bone is sounded with a No. 15 endodontic file, which has a rubber endodontic stopper. This is done buccally and lingually, at the same locations as the above readings. The distance that the rubber stopper is displaced reflects soft tissue thickness. The soft-tissue widths of the buccal and lingual tissues are combined and subtracted from the ridge width to determine bone thickness.
Figure 5. Ridge mapper used to measure ridge thickness. It penetrates through the soft tissue.
Figure 6. Mandibular ridge gets wider apically.
Tissue mapping provides an accurate assessment of bone thickness at different levels of the alveolar ridge and often precludes the need for a CT scan.11 This information can also be transposed to a model of the ridge. Cut the cast in cross section and draw the measurements on the cast to visualize the relationship between the soft tissue and alveolar bone. Bone thickness can also be evaluated using and an instrument called a ridge mapper (Figure 5) (Salvin Dental Specialties). The above techniques are particularly useful when evaluating a ridge that visually, and upon palpation, appears to be too narrow at the crest to receive implants. However, sounding the bone or a CT scan assessment may reveal that the width of the alveolar ridge expands as you proceed apically (Figure 6).
In the mandible, follow the lingual cortex for orientation, because the labial bone may be resorbed. This is done for safety, but not always for a prosthetic point of reference. The submandibular area should be palpated to assess the degree of lingual undercut. Furthermore, during surgical procedures, the precise degree of undercut can be determined without extensive lingual flap reflection by gently reflecting apically under the full thickness of tissue with a Prichard curette and observing its angle of penetration. A Naber’s 2N probe can also do this with less trauma.
Detecting and Avoiding Injury to the Mental Nerve
Figure 7. Measuring a safety zone for implant placement: alveolar crest to mental foramen.
|Figure 8a. If placement of the probe into the mental foramen on the distal side reveals that the mental canal is patent, then the anterior loop is not present. 8b. If placement of a probe into the mental foramen on the distal side reveals that the mental canal is not patent, then an anterior loop of the mental nerve exists. The nerve must have traversed inferiorly and looped back to the foramen creating an anterior loop. (Reprinted with permission from J Periodontol.)|
When in doubt regarding the position of the mental nerve, the mental foramen should be exposed prior to implant placement to ascertain its position.5,12 First, take a measurement on the radiograph with respect to how far the mental foramen is from the adjacent teeth.5,12 If it is located in the bicuspid area, make a vertical releasing incision mesial to the canine and after the flap is elevated past the mucogingival junction, use wet gauze to push the tissue apically to expose the coronal aspect of the mental foramen. The gauze protects the nerve from being injured, and the periosteal elevator can be used to gently push the gauze apically. A measurement is taken from the alveolar crest to the roof of the foramen with a periodontal probe to determine the height of bone over the mental nerve (Figure 7).
Selection of an implant length should provide for a safety distance of 2 mm from the nerve. This distance minus 2 mm can also be used to safely place an implant anterior, over and posterior to the mental foramen up to the mesial half of the first molar area.5,12 Note: markings on an implant drill do not reflect the true length that the tip of the drill penetrates. The drill tip point usually adds 0.4 mm to 1 mm to the depth of the osteotomy. Therefore, it is essential to be familiar with each manufacturer’s equipment.
When it is necessary to determine if there is an anterior loop to the mental nerve (eg, desire to place an implant mesial to the foramen that is deeper than the safety distance determined above), gently probe the foramen with a curved Nabers 2N probe to assess whether the distal aspect of the foramen is patent.5,12 When it is unblocked, there is no anterior loop (Figure 8). If the distal is closed, then there is an anterior loop. When the mesial is patent, it may reflect the presence of the incisive canal or an anterior loop, and it is not possible to differentiate between the 2 structures by probing.5 When there is uncertainty, regarding the presence of an anterior loop, it may be prudent to follow Solar’s recommendation13 of staying at least 6 mm anterior to the mental foramen when placing an implant that is deeper than the determined safety distance.
If a guided bone regeneration procedure is done in the foraminal area and the flap needs to be advanced, buccal periosteal fenestration should be limited in depth to one mm, the width of the bevel on a No. 15 blade, to facilitate release of the flap. Avoid dissecting deeply into the tissue over or anterior to the mental foramen, because branches of the mental nerve are within the tissue. If additional flap advancement is needed in the foraminal area, locate the nerve, and then elevate a full thickness flap that contains the nerve fibers, posterior, anterior and apical to the mental foramen to facilitate flap advancement.
|Figure 9. Surgical guide to replace tooth No. 30. Lingual contour is present and brought buccally to the center of the tooth. A groove is placed to guide mesiodistal osteotomy development. Teeth Nos. 19 to 21 are also being replaced.|
They can be constructed numerous ways.14 A simple method is to design one that engages teeth adjacent to the edentulous area for retention and incorporates only the buccal or lingual contour of the future restoration at the site to receive the implant.15 At this site, the buccal or lingual contours could be widened in acrylic to demarcate the precise buccolingual location of the osteotomy. In addition, a groove should be placed in the acrylic denoting the mesiodistal position of the future implant (Figure 9).
Sterilize No. 2 pencils and use then to mark the alveolar ridge. It saves a lot of time when initiating an osteotomy. It is also efficient to outline on bone the location of the osteotomy for a lateral window sinus lift. In this regard, drawing the root of the tooth anterior to the lateral window on the bone may provide additional orientation, denoting the mesiodistal position of the future implant.
Numerous studies have provided biologic rationales for procedures associated with implant dentistry. In addition, many techniques, and subsequently their modifications, were developed to enhance implant placement. Some of these ideas have appeared in the literature and others have not been published. This 4-part paper reviews a variety of clinical techniques and facts referred to as “clinical pearls” that can be utilized to improve the planning, insertion, and monitoring of dental implants.
- Greenstein G. Advances in periodontal disease diagnosis. Int J Periodontics Restorative Dent. 1990;10:350-375.
- Atassi F. Periimplant probing: positives and negatives. Implant Dent. 2002;11:356-362.
- Nasjleti CE, Caffesse RG, Castelli WA, et al. Healing after tooth reimplantation in monkeys. A radioautographic study. Oral Surg Oral Med Oral Pathol. 1975;39:361-375.
- Thomson EM. Radiation safety update. Contemp Oral Hyg. 2006;10-17.
- Misch CE. Dental Implant Prosthetics. St. Louis, Mo: Mosby-Elsevier; 2005:145-153.
- DENTISPLY RINN. XCP instrumentation kits. rinncorp.com/catalog_filmhold_kits.shtml. Accessed February 19, 2010.
- Gelb DA. Gelb depth gauge: A diagnostic aid in implant placement. Int J Periodontics Restorative Dent. 1992;12:300-309.
- Sonick M, Abrahams J, Faiella RA. A comparison of the accuracy of periapical, panoramic, and computerized tomographic radiographs in locating the mandibular canal. Int J Oral Maxillofac Implants. 1994;9:455-460.
- Littner MM, Kaffe I, Tamse A, et al. Relationship between the apices of the lower molars and mandibular canal—a radiographic study. Oral Surg Oral Med Oral Pathol. 1986;62:595-602.
- Sethi A, Kaus T. Practical Implant Dentistry: Diagnostic, Surgical, Restorative and Technical Aspects of Aesthetic and Functional Harmony. Chicago, Ill: Quintessence Publishing Co; 2005:23-25.
- Wilson DJ. Ridge mapping for determination of alveolar ridge width. Int J Oral Maxillofac Implants. 1989;4:41-43.
- Greenstein G, Tarnow D. The mental foramen and nerve: clinical and anatomical factors related to dental implant placement: a literature review. J Periodontol. 2006;77:1933-1943.
- Solar P, Ulm C, Frey G, et al. A classification of the intraosseous paths of the mental nerve. Int J Oral Maxillofac Implants. 1994;9:339-344.
- Greenstein G, Cavallaro J. The relationship between biologic concepts and fabrication of surgical guides for dental implant placement. Compend Contin Educ Dent. 2007;28:196-203.
- Shepherd NJ. A general dentist’s guide to proper dental implant placement from an oral surgeon’s perspective. Compend Contin Educ Dent. 1996;17:118-120.
Disclosure: Dr. Greenstein reports no conflicts of interest.
Disclosure: Dr. Cavallaro reports no conflicts of interest.
Disclosure: Dr. Tarnow reports no conflicts of interest.
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