Distribution of Bone Quality in Patients Receiving Endosseous Dental Implants

J OralMaxlllolac Surg 55:38·45, 1997, Suppl 5

Distribution of Bone Quality in Patients Receiving Endosseous Dental Implants RICHARD S. TRUHLAR, DDS,· IRA H. ORENSTEIN, DDS,t HAROLD F. MORRIS, DDS, MS,:J: AND SHIGERU OCHI, PHD§ Knowledge of the distribution of bone quality in the various jaw regions assists the clinician in dental implant treatment planning. Bone quality was assessed with radiographs and tactile sensation for 2,839 implants at the time of placement into four anatomic regions of the jaw. The Lekholm-Zarb classification system was used. Overall, bone quality types 1 and 4 were found much less frequently than types 2 and 3. Although variations in density existed in each region, quality 2 bone dominated the mandible, and quality 3 bone was more prevalent in the maxilla. For both anterior and posterior jaw regions, types 2 and 3 bone predominated. The anterior mandible had the densest bone, followed by the posterior mandible, anterior maxilla, and posterior maxilla.

The long-term clinical success of dental implants is highly influenced by both the quality and quantity of available bone.!" Reports indicate a higher survival rate of dental implants in lower jaws. which has been ascribed to better bone quality and quantity in the anterior mandible.Y" Dense bone increases the percentage of bone-implant contact and provides greater initial stability to the implant during the healing period after surgery. Furthermore. such bone structure permits better distribution of the stresses that occur at the implantbone interface during function. Stimulation of bone within physiologic limits may produce an increase in osseous density at the implant-bone interface.":" Physiologic stimulation of less dense bone, with its numerous marrow spaces, does not result in the same

favorable stress distribution as that found in more dense bone. When implants are placed in bone of lesser density, the principle of progressive prosthetic loading may be especially significant. Other facets of implant rehabilitation affected by bone quality include drilling rate and sequence, use of a bone tap. countersinking, length and number of implants placed, healing time, occlusal scheme, and the final prosthetic treatment plan." For example, it is widely accepted that dense bone is best prepared using higher bur speeds, intermittent pressure. copious irrigation, and intermediate drill widths." Misch 12 has suggested that bone density also influences the rate of healing. thereby allowing a clinician to project more accurately the waiting period between implant placement and delivery of the definitive prosthesis. Albrektsson et al" discussed six parameters that need to be controlled for rigid implant fixation and proper osseointegration to occur: the biocompatibility, design, and surface conditions of the implant; the condition of the recipient bone bed; the surgicallechnique; and the loading conditions. Unfortunately, the clinician has little control over the variable of bone quality. Bone volume and relative bone density can be determined and quantified with computed tomography (CT) scanning and other sophisticated radiological techniques. However. the clinician should be prepared to encounter and manage any bone type. Prior knowledge of bone quality prevalent in various anatomic regions of the mouth will assist the clinician with the treatment planning stages of implant therapy. In 1991. the Dental Implant Clinical Research Group (DICRG) initiated a major comprehensive, multicen-

... Clinical Investigator. Dental Implant Clinical Research Group; Staff Periodontist. Department of Veterans Affairs Medical Center, Northport, NY;Clinical A~sistant Professor. Department of Periodontics, School of Dental Medicine. State University of New York, Stony Brook. t Clinical Investigator, Dental Implant Clinical Research Group; Staff Dentist, Department of Veterans Affairs Medical Center. Bronx. NY; Assistant Clinical Professor. Columbia University School of Dental and Oral Surgery. Codirector, DentalClinicalResearch Center; ProjectCodirector, Dental Implant Clinical Research Group, Department of Veterans Affairs Medical Center, Dental Research. Ann Arbor. MI. § Codirector. DentalClinicalResearch Center;ProjectCodirector. Dental Implant Clinical Research Group. Department of Veterans Affairs Medical Center. Dental Research. Ann Arbor, MI. Address correspondence and reprint requests to Dr Morris: Departmentof Veterans AffairsMedical Center,Dental Research (154), 2215 Fuller Rd, Ann Arbor, MI 48105.

*

This Is a US government work. There are no restrictions on Its

use.

0278·2391/97/5512-5009$0.00/0

38

39

TRUHLAR ET AL

ter, multidisciplinary long-term clinical study to investigate the influence of implant design, application, and site of placement on clinical success. 19 The study consists of 30 Department of Veterans Affairs Medical Centers and several research universities. An interim study report, published in 1994,20 reported on stage I data for 1935 implants. The aim of this report is to describe the final distribution of bone quality in the various regions of the jaws for all enrolled study cases, totaling 2,839 individual implants.

As part of the comprehensive studies by the DICRG, the quality of bone at each implant site was recorded at the time of placement surgery, and the prevalence of various bone qualities was later tabulated. The Lekholm-Zarb classification system" was used to assess quality of bone. In their system (Fig 0, there are four different categories: quality I (Q-l) bone is composed largely of dense, homogenous cortical bone with a small core of trabecular bone; quality 2 (Q-2) bone exhibits a large, dense layer of cortical bone that surrounds a dense trabecular core; quality 3 (Q-3) bone has a thinner layer of cortical bone around a dense trabecular core; and quality 4 (Q-4) bone has a thin cortical layer surrounding a low-density trabecular core. The surgeon evaluated the quality of bone using both radiographs and tactile sensations of cutting resistance and force required during the preparation of the osteotomy site (Fig 2). Bone quality classification was recorded, along with type of implant, its approximate tooth location, and its length and diameter. Randomization determined the implants assigned to each case in the five research strata (Table I), designated as UCE, maxillary completely edentulous cases; UP, maxillary posterior partially edentulous cases; UST, maxillary anterior single tooth cases; LCE, mandibular completely edentulous cases; and LP, mandibular posterior partially edentulous cases.

Patients and Methods

Results

Selection of the 30 participating VAMC implant research centers followed careful screening of 55 interested medical centers using the following criteria: I) the training credentials and experience of each member of the implant team were adequate to conduct the study; 2) the team must consist of no less than two trained investigators; 3) the investigator who placed the implants was not the one to complete the followup evaluations; and 4) all study participants would undergo comprehensive training and standardization sessions before placing, restoring, and maintaining implants. Furthermore, investigators must continue to undergo annual retraining and standardization testing. After selection of the medical centers, more than 85 clinical investigators were trained and standardized in I) clinical protocols, 2) application of the project evaluation criteria, and 3) data collection procedures. As part of the project design, the 30 medical centers were randomized to one of two independent study groups to aid in later statistical analyses of the data. Two dental schools were subsequently added to one of the study groups. All potential patients were carefully screened before entry into the study. Both a comprehensive medical/ dental history and a dental/clinical evaluation were completed. Inclusion and exclusion criteria have been reported previously."

A total of 2,910 implants have been placed and recorded in the DICRG database as of May 1995. Sixtythree of these implants were replacements for those that failed. The remaining 2,847 implants placed at first surgery are used as the denominator in all computations of percentages in which characteristics at implant placement are tabulated. The total number of implants tabulated was 2,839, after eight implants were dropped from the study analysis because of missing bone quality data. Percentage bone quality distributions for the mouth as a whole, and broken out by study groups A and B, are presented in Table 2. Q-2 and Q-3 bone were found at most implant sites, with Q-I and Q-4 bone found infrequently. To promote simplicity, data for study groups A and B are combined for the remainder of this report.

1

2

3

4

FIGURE I. Bone quality as defined by Lekholm and Zarb." Q-I. dense homogenous cortical bone with a small trabecular core; Q-2. large. dense layer of cortical bone surrounding dense trabecular core; Q-3, thinner layer of cortical bone around dense trabecular core; Q4, thin cortical layer surrounding low-density trabecular core.

BONE QUALITY BY ARCH AND POSITION Table 2 summarizes the distribution of bone quality by arch and position of implant placement. Bone quality prevalence by jaw arch shows Q-2 bone predominated in the mandible (mean bone quality of 2.14, SO = 0.65) and Q-3 in the maxilla (mean bone quality of 2.83, SO = 0.65). In anterior and posterior jaw positions, Q-2 and Q-3 bone were most prevalent.

40

INTRAORAL BONE QUALITY DISTRIBUTION

FIGURE 2. Radiographic evaluation of hone quality. A. Panoramic x-ray film of a fully edentulous patient showing <)-2 hone in the anterior mandible. 1J. Reformatted CT scan showing <)-1 hone in the anterior mandible. C, Reformatted CT scan showing <)-2 hone in the anterior maxilla. D. Reformatted CT scan showing <)-1 hone in the posterior maxilla. E, Reformatted CT scan showing <)-4 hone in the posterior maxilla.

Table 1.

Study Strata, Implant Design and Materials, and Prosthetic Application

Stratum

Number of Implants

Maxillary fully edentulous (VCE)

5 or 6

Maxillary posterior

2 or :\

partially edentulous (UP) Maxillary anterior single tooth (UST) Mandibular fully edentulous (I.CE) Mandibular posterior partially edentulous (I.P)

5 or 6

Implant Ilc'iMIl

Name"

Marcriul

Grooved Screw Screw Grooved Cylinder Grooved

Micro-Vent Screw-Vent Screw-Vent Micro-Vent Bio-Vent Micro-Vent

IIA-coated HA-coated Titanium-CP HA-coated HA-coated HA-coated

Basket

Cure-Vent Screw-Vent Bio-Vent Core-Vent Bio-Vent

Ti alloy Ti alloy HA-coated Ti alloy IIA-coateu

Screw 2 or :\

Cylinder Basket Cylinder

Application Bar-retained ovcrdenturc (implant supported only) Fixed-detachable partial denture

Single crown (temporary cement: Fixcd-dctachahlc complete denture Fixed-detachable partial denture

NOTE. CP, commercially pure; HA, hydroxyapatite, • Micro-Vent, Screw-Vent. Bin-Vent. and Core-Vent implants arc Spectra-System products (Core-Vent Corporation, Las Vegas, NV).

41

TRUHLAR ET AL

100%

j

..

en

c .!! a.

....5

.0-4 00-3 .0-2

80%

_0-1

60%

0

~ 40%

ii

::2

a

•c

20%

~

1994 1996 Maxilla

1994 1996 Mandible

FIGURE 3. Comparison of DICRG bone quality data. 1994 (n = 1,935) vs 19l)6 (n = 2.1139). Maxillary implants: 774 in 1994; 1,237 in 1996. Mandibular implants: 1.161 in 1994; 1,602 in 1996.

Figure 3 graphically compares the bone quality data published by the DICRG in 1994 20 with the current report. As can be observed, the percentage distribution of types of bone quality in the current report differs very little from that of the 1994 D1CRG report. even with the addition of 904 implants in the current report, almost 50% more implants. Bone quality distribution and the mean bone quality found in each research stratum as shown in Table 3. Overall, Q-I and Q-4 bone were found in a minority of instances. In UCE cases, Q-3 bone was found most often. In UP cases. Q-3 bone also predominated. In UST cases, an abundance of both Q-2 and Q-3 bone was noted, with Q-3 bone predominating. In LCE cases. mainly Q-2 bone was present. In LP cases, Q2 bone was predominant, but a substantial amount of Q-3 bone was also encountered. BONE QUALITY, INITIAL IMPLANT MOBILITY, AND USE OFA BONE TAl' Table 4 shows the relation between implant mobility at time of placement and bone quality. At the time of Table 2. Distribution of Bone Quality of Implant Sites by Study Group and Site of Implant Placement (N = 2,839) Location (no. of implants) All sites Group A (1.351) Group B (10488) Pooled data (VDlJ) Arch sites. pooled data Maxillary arch (1,2.~7) Mandibular arch (1.602) Jaw sites. pooled data Anterior jaw (1.712) Posterior jaw (1.127)

Q-I

Q-2

Q-3

Q-4

('7r)

('h')

('h)

('ho)

12.7 45.4 32.6 5.5 45.7 41.4 X.lJ 45.5 37.2

9.3 7.4 8.3

1.1 26.4 56.3 16.2 15.0 60,4 22.5 2.2 10.7 46,4 35.6 6.2 44.2 39.7

7.2 9.9

Mean Bone Quality 2: SD

Table 3. Distribution of Bone Quality of Implant Sites by Research Stratum (N = 2,839) Research Stratum (no. of implants) Maxillary anterior • UCE (601) Maxi llary posterior. UP (401) Maxillary anterior single tooth. UST (235) Mandibular anterior, LeE (876) Mandibular posterior. LP

Q·1

Q-2

Q-3

Q-4

(%)

(%)

(%)

(%)

0.5

24

59

16

2.91 :t 0.64

1.5

23

53

23

2.98 :t 0.72

1.7

37

55

5.5

2.65 :t 0.61

64

14

1.8

1.98 :t 0.65

56

33

2.6

2.30 :t 0.66

20

8.8

(726)

Mean Bone Quality :t SO

implant placement, 2.8% of those in Q-I bone were mobile, as were 2.3% of Q-2 implants, 3.6% of Q-3 implants, and 6.8% of Q-4 implants. Of the 88 implants that were mobile at stage I surgery, 37 (42%) were in Q-3 bone and 15 (17%) were in type IV bone. Table 5 reflects the use of a bone tap for 1,270 threaded fixtures (Screw-Vent and Core-Vent, Core-Vent Corporation, Las Vegas, NV). A bone tap was used during installation of 131 fixtures in Q-3 bone (31.5%) and nine fixtures in Q-4 bone (11.1 %). BONE QUALITY BY PATIENT CHARACTERISTICS The relation of bone quality to health status showed a significant difference (chi-square. P < .00l) as shown in Table 6. Those patients classified as "healthy" had a lower proportion of bone quality QI and Q-2 than those with mild systemic disease. Comparison of bone quality against age (Table 7) showed a slight tendency toward a higher (Q-I + Q-2)/(Q-3 + Q-4) ratio with increasing age. However, these differences were not statistically significant. Analysis of bone quality by gender is shown in Table 8. Because the number of females was much smaller than the number of males in the study population, a comparison is probably not valid. However, in males the prevalence of Q-I bone and Q-4 bone was similar, but in females, Q-I bone was more prevalent than Q4 bone.

Table 4. Relation Between Implant Mobility at. Placement and Bone Quality of Implant Sites (N = 2,839) 2.83 :t 0.65 2.14 :t O.M

Mobility

Q-I

Q-2

Q-3

Q-4

No (2.751) Yes (88)

246 7

1.264 29

1,020

221 15

37

42

INTRAORAL BONE QUALITY DISTRIBUTION

Table 8. Relation Between U.e of a Bone Tap and Bone Quality of the Implant Site. (N = 1.270 Threaded Implanu)

Table 7. Relation Between Patient Age and Bone Quality of Implant Site. (N = 2.834 Implants)

Bone Tap Used

Q-I

Q-2

Q-3

Q-4

No (675) Yes (595)

47 99

272

284 131

72

356

9

The computation of bone quality by race is shown in Table 9. As a reflection of the older veteran population, most of the patients receiving implants were white. Chi-square analysis showed a significant difference (P < .041) between white patients and African American patients in the distribution of types of bone quality. Discussion

The stage I results of the DICRG study support current beliefs concerning the general distribution of types of bone density in edentulous and partially edentulous patients. Although the determination of bone density by radiographs and tactile sensations is biased by operator subjectivity, the results in this project are strengthened by the use of multiple investigators and a large sample size. This is well demonstrated by consistency of the findings between the 1994 and the 1996 pooled data. Accurate preoperative evaluation of bone quality is useful to the clinician in surgical and prosthetic treatment planning and may assist in predicting the outcome for treatment. Recent in vitro investigations are attempting to develop a more objective determination of the bone density at osteotomy sites by measuring the resistance to drilling and cutting torque in Joules per cubic millimeter, the current drawn by the electric motor. 22•23 At the current state of development, such devices appear to hold most promise in the future training of clinicians, to help them calibrate their subjective determinations of bone quality. As would be expected, the greatest percentage of implants that were mobile at the time of placement were found in the poorer bone qualities. Use of a bone tap in Q-3 and Q-4 bone may potentiate overpreparation and stripping of the osteotomy site, resulting in

Table 8. Relation Between Sy.temlc Health Statu. and Bone Quality of Implant Site. (N = 2.828 Implant.) Patient Health (no. of implants) Healthy (1.311) Mild disease (1,447) Severe disease (71)

Q-I (%)

Q-2 (%)

Q-3 (%)

Q-4 (%)

7.2 II

44

39 35 39

9.3 6.5 28

47 32

Patient Age (no. of implants) ".30 31-40 41-50 51-60 61-70 71-80 81-90

(73) (165) (573) (503) (919) (580) (21)

Q-I (%)

Q-2 (%)

Q-3 (%)

Q-4 ('if)

4.1

41 47 49 38 46 48 71

49 45 36 41 35 36 14

5.5 7.9 7.5 II 7.8 7.9 4.8

7.7 9.9 II 8.8 9.5

mobility at the time of placement, but the increased incidence of mobility at time of placement in Q-3 and Q-4 bone may be attributable only in part to tapping. Other factors that may come to bear on implant mobility in low-density bone include drill run-out, or "wobble," and operator alignment error, both of which can create an ovoid rather than round osteotomy site. The higher incidence of Q-I and Q-2 bone in patients with mild systemic disease may be related to the assumption that there is a positive correlation between systemic disease and age. 24 •25 As alveolar bone resorbs with age, the more dense basal bone predominates in the anterior mandible, creating a higher percentage of Q-l and Q-2 bone. The proportion of healthy patients having lower bone quality also might be influenced by patient selection factors that may screen more carefully those patients with mild systemic disease. That is. there may be a selection bias by the implant team for patients with mild systemic disease to have sufficient quality bone before the case is accepted for treatment. A finding of interest in patients with severe systemic disease is the lack of Q-l bone and a shift toward Q-3 and Q4 bone. Although this bone quality distribution may be related to the nutritional or disease states of the patients and the medications used to treat these diseases, chronic steroid use and other medications known to affect bone density were not common in this group. Most of the patients in the severe systemic disease category presented with various forms of cardiovascular disease. This is consistent with other published reports about veteran populations." In the current study, these patients were typically medicated with various combinations of calcium channel blockers, angiotenTable 8. Relation Between Patient Gender and Bone Quality of Implant Site. (N = 2.838 Implants) Patient Gender (no. of implants)

Q-t (%)

Q-2 (%)

Male (2,673) Female (166)

8.6 13

45 52

Q-3

('Yr,)

31\ 30

Q_4(tif)

1\.5 4.1\

TRUHLAR ET AL

Table 9.

43

Relation Between Race and Bone Quality of Implant Sites (N Racial Group (no. of implants)

= 2,839 Implants)

Q-I (%)

Q-2 (%)

Q-3 (%)

Q-4 (%)

9.1

45 42 45 67 85 64

37 40 43 33 7.7 36

8.9 6.0 9.3

White (2.245) African American (402) Latin American (118) Asian (39) Native American (13) Other* (22)

II

2.5

7.7

* Patients who preferred not to be identified in a category or who were uncertain of the category in which to place themselves.

sin-converting enzyme inhibitors, long and short-acting nitrates, and, occasionally, diuretics and ,a-blockers. In this study, it is difficult to accurately correlate bone quality with gender, because the veteran population is predominantly male. Most women in the study represented dental school populations, and the two population pools may not be similar. Reflecting the older veteran population, most patients in this study were white. The data do, however, suggest a clinically similar pattern of bone quality among the races that are well represented (white, black, Asian). DICRG data and those of other investigators concerning bone quality are compared in Table 10. Comparison by meta-analysis of bone quality prevalence data of the DICRG and other studies shows the maxillary values of the DICRG to be almost identical to the pooled data from Friberg et al,? Johns et aI,S and Quirynen et al.27 For the mandible, DICRG data show a higher prevalence of Q-l and Q-2 bone and a lower prevalence of Q-3 and Q-4 bone. This difference may be explained by the fact that patients treated by Johns et al had bone with insufficient quality to support fixed prostheses and were restored with overdentures. The data of Quirynen et al, for patients restored with fixed prostheses, more closely parallel those of the DICRG. Laohapand," using the same criteria to evaluate bone density at 321 implant sites, organized his data as follows: Q-l and Q-2 bone were called "good"; Q-3 and Q-4 bone were called "poor." 28 When DICRG data are regrouped in this manner, results for Table 10.

the mandible are strikingly similar. However, for both the anterior and posterior segments in the maxilla, the DICRG found a significantly lower amount of good quality bone (12% fewer good bone quality cases anteriorly and 26% fewer posteriorly). These discrepancies may reflect differences in operator subjectivity, selection criteria, or actual patient populations. Manufacturers and clinicians are considering the importance of bone quality and shape in relation to the design, surface characteristics, and placement techniques of dental implants. Nobelpharma (Nobelpharma-AB, Goteborg, Sweden) introduced self-tapping implants in 1983 for use in situations in which soft bone quality is present. 29 They continued with further modifications and developed a wider diameter implant (5.0 mm) that Langer et al 30 described as useful in areas of poor bone quality. Wider implants may increase interfacial bicortical stabilization. Hydroxyapatite (HA) and titanium plasma-sprayed implant surfaces have been developed in an effort to improve osseointegration, compared with commercially pure titanium SCrew implants, when used in poor quality bone. Engquist et al" placed 191 maxillary and 148 mandibular implants (Nobelpharma AB, Goteborg, Sweden) supporting overdentures. Of the 38 maxillary implants (20%) that failed to osseointegrate at uncovering, 31 were in Q-4 bone. In this investigation, 78% of the total implant failures occurred in Q-4 bone. Jaffin and Berman" reported the loss of 23 of 52 Branemark implants (44%) placed in Q-4 bone in the maxilla; II of 30 implants (37%) placed in Q-4 bone in

Distribution of Bone Quality of Implant Sites by Jaw Arch: Comparison of Various Studl.s Mandible

Maxilla Study

Q-l(%)

Q-2(%)

Q-3 (%)

Q-4(%)

Q-I (%)

Q-2 (%)

Q-3(%)

Q-4 (%)

Johns et al 5 Friberg et al? Quirynen et al27 Average of above three DlCRG 199420 DlCRG 1996

0 I 2 I 1 I.l

13 24 37 25 27 26.4

60 60 50 57 55 56.3

27 15 10 17 17 16.2

7 4 10 7 15 15.0

42 49 65 52 61 60.4

45 34 25 35 22 22.5

7 13 0 7 3 2.2

44 the posterior mandible; and 2 of 20 implants (10%) placed in Q·4 bone anterior to the mental foramina, for an overall failure rate of 35% in Q-4 bone. They experienced only a 3% loss at the time of uncovering of all implants placed in Q-I to Q-3 bone. Lozada" reported on the success or failure of 109 uncoated titanium screw implants (Steri-Oss) and 110 HAcoated titanium screw implants (Steri-Oss) in what he classified as type 4 bone. In the maxillary arch, 32.6% of uncoated implants failed compared with 14.7% for the HA-coated implants. Saadoun and LeGall 32 studied 673 Steri-Oss (Bausch and Lomb, Yorba Linda, CA) implants (titanium screws, HA-titanium screws, and HA-titanium cylinders) during a 5-year period and recommended the choice of design be based on implant length, bone quality, and anatomic region. They recommended that the closer the bone is to type 4, the greater the indication for HA-titanium cylinders. Fugazotto et at33 placed 1,363 titanium plasma-sprayed cylindrical implants (Interpore IMZ, Steri-Oss, Irvine, CA), 513 of which were inserted in Q-4 bone. The success rate dropped from 97.4% overall to 95.7% for Q-4 bone (22 failures in Q-4 bone out of a total of 34). When evaluating the distribution of bone quality, it becomes apparent why the maxilla, particularly in the posterior region, often presents with higher implant failure rates. Several additional compromising factors probably contribute to this region's poorer prognosis. Generally, the posterior maxilla receives the shortest implants, unless there are sinus grafting procedures. This, coupled with the buccal cantilevering of the final prosthesis often needed to maintain arch form, and the increased occlusal forces found in the posterior jaw mandates precise treatment planning strategies for the posterior maxilla. Conversely, the anterior mandible generally has the highest-quality bone and can accept longer implants because of the lack of anatomic obstacles. As a result, the prognosis for well-designed mandibular prostheses supported by anterior implants is usually very favorable. Knowledge of anticipated bone density before beginning implant therapy may assist clinicians with optimization of treatment strategies to achieve predictable and stable long-term results. Data from this and previous dental implant trials suggest that bone quality of the maxilla and mandible is controlled by independent physiologic variables.

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INTRAORAL BONE QUALITY DISTRIBUTION 3. Mericske-Stern K: Overdentures with roots or implants for elderly patients. A comparison. J Prosthet Dent 72:543. 1994 4. Bahat 0: Treatment planning and placement of implants in the posterior maxillae: Report of 732 consecutive Nobelpharma implants. Int J Oral Maxillofac Implants 8: 151. 1993 5. Johns RB. Jemt T. Heath MR. et al: A multicenter study of overdentures supported by Branemark implants. Int J Oral Maxillofac Implants 7:513. 1992 6. Jaftin RA. Berman CL: The excessive loss of Branemark fixtures in type IV bone: A 5-year analysis. J Periodontol 62:2. 1991 7. Friberg B. Jemt T. Lekholm U: Early failures in 4.641 consccutively placed Brimemark dental implants: A study from stage I surgery to the connection of completed prostheses. Int J Oral Maxillofac Implants 6:142. 1991 8. Engquist B. Bergendal T. Kallus T. et al: A retrospective multicenter evaluation of osseointegrated implants supporting overdentures. Int J Oral Maxillofac Implants 3: 129. 19XX 9. Bass SL. Triplett RG: The effects of preoperative resorption and jaw anatomy on implant success. Int J Oral Maxillofac Implants 6:193. 1991 10. Morris HF. Ochi S. Gillette W. et al: Bone quality and implant integration during follow-up in the DICRG study. J Dent Res 74(Special Issue):495. 1995 (abstr) II. Arpak N. Niedermeier W. Nergiz I. et al: Morphometry of the peri implant of immediate and late endosseous implants. J Dent Res 74(Special Issue):414. 1995 (abstr 110) 12. Misch CE: Density of bone: Effect on treatment plans. surgical approach. healing, and progressive bone loading. Int J Oral Implantol 6:23. 1990 13. Carter DR: Mechanical loading histories and cortical bone remodeling. Calcif Tissue Int 36:S 19. 1984 14. Carter DR. Caler WE: Cycle-dependent and time-dependent bone fracture with repeated loading. J Biomech Eng 105: 166. 1983 15. Carter DR. Caler WE. Spengler DM, et al: Fatigue behavior of adult cortical bone: The influence of mean strain and strain range. Acta Orthop Scand 52:481. 19XI 16. Misch CE: Density of bone: Effect on treatment planning. surgical approach. and healing. in Misch CE (ed): Contemporary Implant Dentistry. St Louis. MO. Mosby. 1993. pp 46lJ-4X5 17. Adell R. Lekholm U. Branernark P-I: Surgical procedures, ill Brilnemark P-I. Zarb GA. Albrektsson T (eds): Tissue-Integrated Prostheses: Osseointegration in Clinical Dentistry. Chicago. IL. Quintessence. 1985. pp 211-232 18. Albrektsson T. Brllnemark P-I. Hansson H-A. et al: Osseointegrated titanium implants: Requirements for ensuring a longlasting. direct bone-to-implant anchorage in man. Acta Orthop Scand 52:155. 1981 19. Morris HF. Ochi S. Dental Implant Clinical Research Group (Planning Committee): The influence of implant design, application. and site on clinical performance and crestal bone: A multicenter. multidisciplinary clinical study. Implant Dent 1:49, 1992 20. Orenstein IH. Synan WJ. Truhlar RS. et al: Bone quality in patients receiving endosseous dental implants: DlCRG interim report no. t. Implant Dent 3:90. 1994 21. Lekholm U. Zarb GA: Patient selection and preparation. ill Branemark P-I. Zarb GA. Albrektsson T (eds): Tissue-Integrated Prostheses: Osseointegration in Clinical Dentistry. Chicago. IL. Quintessence. 1985. pp 199-209 22. Johansson P. Strid K-G: Assessment of bone quality from cutting resistance during implant surgery. Int J Oral Maxillofuc Implants 9:279. 1994 23. Friberg B, Sennerby L. Roos J. et al: Evaluation of bone density using cutting resistance measurements and microradiography: An in vitro study in pig ribs. Clin Oral Implants Res 6: 1M. 1995 24. Jastak JT. Cowan FF: Patients at risk. Dent Clin North Am 17:363,1973 25. Suomi JD. Horowitz HS. Barbano JP: Self-reported systemic conditions in an adult study population. J Dent Res 54: lOn, 1975 26. Nery EB. Meister F. Ellinger RF. et al: Prevalence of medical problems in periodontal patients obtained from three different populations. J Periodontol 58:564. 1987 27. Quirynen M. Naert I. van Steenberghe D. Nys L: A study of

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5H') consecutive implants supporting complete fixed prostheses. Part I: Periodontal aspects. J Prosthct Dent 68:655, 1992 28, Luohapand 1': The Pcriotcst as an Objective Means to Assess Implant Stability. l.cuvcn. Belgium, Catholic University of Leuvcn, 1')91 29. Friberg B, Grondahl K, l.ckholm U: A new sell-tapping Branemark implant: Clinical and radiographic evaluation. Int J Oral Maxillotac Implants 7:80, 1')92 30, Langer B, Langer L, Herrmann I, ct al: The wide fixture: A solution for special bone situations and a rescue for the

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