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Bone resorption around fixtures in edentulous patients treated with mandibular fixed tissue-integrated prostheses
MAXILLOFACIAL
PROSTHETICS
. DENTAL IMPLANTS
SECTIONEDIT0R.S I. KENNETH
,4DISMAN
RONALD
P. DESJARDINS
Bone resorption around fixtures in edentulous patients treated with mandibular fixed tissue-integrated prostheses Lars W. Lindquist, D.D.S.,* Birger Rockier, D.D.S.,** Gunnar E. Carlsson, D.D.S., Odont.Dr.*** University
of G8teborg,
Faculty
of Odontology,
Gijteborg,
Sweden
T
he gradual reduction of edentulous residual alveolar bone supporting complete dentures is a major oral disease entity.’ Several longitudinal studies have indicated that morphologic changes of denture-bearing regions are inevitable even if they show great individual variation.2-5 Changes of the prosthesis support, especially in the mandible, may compromise denture wearing and masticatory functions. 6,7The amount of bone reduction is generally greater in the mandible, which implies that the mandibular denture usually poses greater clinical problems for the patient and the prosthodontist.* The successful replacement of lost natural teeth by tissueintegrated dental implants is therefore an exciting improvement in clinical dentistry.9 The experimental background and the biologic and functional successwith fixed prostheses on osseointegrated implants have been well documented.‘O-‘5 Of particular interest is the reaction of the bone after implant therapy. The fixed prosthesis on osseointegrated implants provides a different type of stimulation to the bone that a conventional denture. It has been reported9 than the mean annual “marginal bone loss” around osseointegrated fixtures is at most 0.1 mm, which is substantially less than that under conventional dentures.lV5 This article analyses bone resorption around fixtures in association with treatment of the edentulous mandible with fixed prosthesis on tissue-integrated implants.
MATERIAL
AND METHODS
Forty-six patients comprising two groups of patients, 25 and 21 persons (Table I), were treated with mandibular fixed prostheses on tissue-integrated implants (TIPS) according to principles described elsewhere.9s’6 All treatment was performed by the same prosthodontist and the laboratory work was done by the same dental technician throughout the period of investigation. After TIP treatment the first group of patients (group 1) has *Chief, Clinic of Prosthodontics, Community Dental Health Service, GGtehorg, Sweden. **Assistant Professor, Department of Oral Radiology. ***Professor and Chairman, Department of Prosthetic Dentistry. THE JOURNAL
OF PROSTHETIC
DENTISTRY
and
Table I. Age and sex distribution
of the two patient groups at the final follow-up Age Group 1
2
Sex
-40
41-50
51-a
61-65
F M
2 1
3 2
11
3 1
F
2
M
1
2 2
10 1
2
Total
3
19 6 25 17
-
a
21
been observed for 5% to 6 years and group 2 for approximately 3 to 4 years. The patients were originally selected for the two matched groups with respect to age, sex, and degree of mandibular resorption.’ All of the patients received the same type of treatment and the only difference between the groups was the length of the follow-up period.
Radiographic examination
and measurements
A stereoscopic radiographic technique has been used according to principles described previously.“,‘* The radiographic examination was routinely performed 1 week after the abutment operation, 6 and 12 months postoperatively, and once every 12 months thereafter. The original, l- and 3-year and final intraoral radiographs were used in this study. The radiographs were inspected with respect to bone loss and change of density and architecture of the bone around the fixtures. The “marginal bone height” (height of the bone anchorage zone, Fig. 1) of each fixture was measured mesially and distally by using the fixture threads as an internal dimensional reference. Each thread is 0.6 mm, but it can distinctly be divided into halfs; thus the measuring unit used was 0.3 mm. The means of the mesial and distal measurements have been used as a value for each fixture.
Other variables Clinical recordings of bite force, chewing efficiency and other masticatory parameters, anamnestic and clini59
LINDQUIST,
ROCKLER,
AND
CARLSSON
0.5 -
1.0 -
0A
0B Fig. 1. Measurement of height of bone anchorage (marginal bone height). Mean of mesial and distal values (M[h, + hJ) was used for each fixture. cal dysfunction indices, attrition and occlusal wear, and degree of bone resorption before TIP treatment (from profile radiographs) were performed according to methods and principles described previously.‘, 15*l6 Oral hygiene was assessedretrospectively from scrutiny of the record of each patient. At each visit during the observation period the oral hygiene level was evaluated according to a 3-point scale: 0 = no visible plaque; 1 = local plaque accumulation (<25% of the visible abutment area); and 2 = general plaque accumulation (>25%). An oral hygiene index was calculated by adding the scores and dividing by the number of visits. The index could thus have values between 0 and 2. The extension of the cantilever part of the prosthesis was measured in millimeters from the distal surface of the most posterior fixture on each side.
Statistical method Significance tests for differences between groups were performed with Pitman’s permutation test.19For correlation analysis the nonparametric Spearman rank correlation test was used.20
RESULTS None of the 276 fixtures was lost during the observation period. The density of the bone around the fixtures seemedin general to increase indicating osseointegration. 60
MM
-0
GROUP
1
-v-Q
GROUP
2
RESORPTION
Fig. 2. Mean values of bone loss around all fixtures in 25 patients followed up for 6 years (group 1) and 21 patients for 3 years (group 2) after treatment with mandibular fixed prosthesis on tissue-integrated implants. The bone loss around the fixtures during the first 3 years after treatment was similar for the two groups (Fig. 2). The greatest loss occurred during the first year (0.40 to 0.45 mm), after which the annual resorption was 0.07 to 0.08 mm. During the next 3 years, group 1 showed a reduction of the bone height of even less magnitude: the mean annual loss for all fixtures from 3 to 6 years was
0.06 mm. The marginal bone loss differed among the various fixtures. The medial fixtures had more bone loss than the posterior ones (Fig. 3). This was a consistent finding in bone groups and it was evident after 1 year. Analysis of various factors influencing the bone loss was performed by dividing the material into subgroups and by correlation tests. Oral hygiene influenced the degree of bone resorption: patients with poor oral hygiene had more bone loss than those with no remarks of their hygiene (Fig. 4). The length of the cantilever extensions tended to be of increasing importance with time for the bone loss of the medial fixtures; after 6 years, seven patients with long cantilevers bilaterally (L 15 mm) had a mean loss around the medial fixtures of 0.95 mm whereas six patients with short cantilevers (<15 mm) had 0.61 mm. The differences for the more posterior fixtures were nonsignificant. The same tendency, not reaching a statistically significant level, was seen in group 2 with a shorter observation period.
Correlations The bone loss around the fixtures was tested for correlation to a series of recorded factors. The variable most strongly correlated to bone loss in group 1 was poor oral hygiene (Table II). This finding was also verified in group 2. Functional recordings such as bite force, chewing efficiency and other registrations related to mastication, and anamnestic and clinical dysfunction JANUARY
1988
VOLUME
59
NUMBER
1
BONE RESORPTION
AROUND
FIXTURES
GROUP I RESORPTION
13
6
6
13
13
6
13
Rl
R2
R3
6
6
13 L2
Ll
13
6 L3
YEARS LOCATION
GROUP II RESORPTION MM
0.5
0B
1
3 R3
1
3 R2
1
3
13
Rl
Fig. 3. Mean values of bone loss around length of observation period.
indices were not significantly
correlated
to bone loss.
Reported tooth clenching and recorded occlusal wear on the prostheses showed relatively strong correlations to bone loss that were significant for single calculations (Table II). The pretreatment degree of mandibular resorption was not significantly correlated to the bone loss around the fixtures. The length of the cantilever extension of the fixed TIP was not significantly correlated to bone loss around the fixtures for any of the parameters included in Table II. The continuing bone loss around some of the fixtures (R2, Vl , V3) from 3 to 6 years in group 1 was positively correlated (p < 0.05) to the length of the cantilever extensions and this was verified for the mean bone loss for all fixtures during 3 to 6 years. In group 2 the correlations were similar but usually they did not reach a statistically significant level.
Ll
1
13
3
YEARS
L3
LOCATION
separate fixtures
according
L2
to location
and
ORAL
RESORPTION
HYGIENE
GOOD
MM
POOR I
1
3
6
YEARS
Fig. 4. Mean bone loss around all fixtures in nine patients with good oral hygiene (no remark of plaque at recall visits during observation period) and nine
patients with poor oral hygiene (frequent remarks of plaque accumulation).
Multivariate
analysis
Multiple stepwise regression analyses were performed with some mean values of bone resorption (0 to 3 years, 0 to 1 year, and 1 year to the final visit) as dependent variables and the following 12 independent variables: THE JOURNAL
OF PROSTHETIC
DENTISTRY
original bone resorption level, oral hygiene, reported clenching of teeth, tooth wear, mucosal ridging, maximal bite force and finger force, bite force as in chewing and forceful biting, mean length of cantilever extensions, and 61
LINDQUIST,
ROCKLER,
AND
CARLSSON
Table II. Spearman rank correlation coefficients between marginal bone loss around osseointegrated fixtures during a 6-year period after treatment and three other factors in 25 patients with mandibular fixed TIP Years O-6
Oral hygiene Occlusal wear Tooth clenching
R3
RZ
Rl
Ll
L2
0.15 0.46’ 0.11
0.44* 0.35 0.41
0.52t 0.05 0.38
0.52t 0.08 0.33
0.53t 0.28 0.34
o-1
o-3
L3
x
x
0.53t 0.26 0.29
0.42’ 0.19 0.27
o.sot 0.32 0.41*
83 and L3 are the most posterior right and left fixtures, Rl and Ll are the most anterior. l 0.01 < p < 0.05. fo.001 < p < .Ol.
Table III. A stepwise multiple
regression
analysis with mean bone loss around mandibular fixtures as dependent variable in 46 TIP patients Variables
Dependent
Independent
F value
R’
A
Oral hygiene Clenching of teeth Mucosal ridgings Clenching of teeth Oral hygiene Oral hygiene Length of cantilever extension
16.3 7.3 2.2 12.5 4.5 5.0 3.4
0.27 0.38 0.41 0.24 0.32 0.11 0.18
B C
A = 0 to 3 years; B = 0 to 1 year; C = 1 year to final visit.
anamnestic and clinical dysfunction index values. In the analysis in both groups taken together, oral hygiene and clenching of teeth were the most strongly correlated independent variables for the first observation periods (Table III). Oral hygiene was also the first independent variable to enter the equation in an analysis with the mean bone loss from the l-year to the final recall visit, and the mean length of the cantilever extension showed the only further significant correlation with that dependent variable (Table III, C’). Similar results were found in separate analyses in the two groups. In addition to the significant variables shown in Table III, bite force values also reached a significant level of correlation with the dependent variables in single analyses in the separate groups.
DISCUSSION The continuous and inevitable bone resorption associated with conventional removable dentures should be contrasted with the results of this study. The most remarkable finding is therefore the extremely small amount of bone resorption that occurred during the first 62
6 years after treatment with fixed tissue-integrated prostheses in previously edentulous mandibles. That no single fixture was lost during the observation period also deserves to be emphasized. ,These results give further evidence of the favorable biologic results this therapy seems to offer.6-16The bone loss in this study is even smaller than reported previously for the first year after prosthesis connection and later.13 This might be explained by the fact that the surgical and prosthetic methods have been refined since the first developmental period, as corroborated in recent reports.21s22The longterm development for osseointegrated fixtures thus appears to be extremely good. With less than 0.1 mm bone loss per year after the postsurgical period, the prognosis for life-long function is evident for most tissue-integrated implants. Oral hygiene was found to be the most important factor associated with marginal bone loss. This finding is not surprising with respect to current periodontal concepts.23 However, the reactions in the marginal soft tissues and the microbiota in the perifixtural pockets seem to differ from those around natural teeth. The soft tissue-titanium relationship perhaps should not be assessed by conventional indices.21,22p24The careful instructions in oral hygiene recommended for TIP patients to avoid compromises in gingival health seem to be necessary also to minimize the bone loss around the fixtures.9s25 According to the analyses, functional and loading factors were also of importance. Parafunctional activity such as bruxism, both as reported tooth clenching and recording of occlusal wear on the prosthesis, led to increased bone loss. The correlation between the length of the cantilever extensions and bite force on one side and some bone loss values on the other side also indicated possible influences of overloading. The multivariate analysis verified that a combination of poor oral hygiene and extensive loading were the factors that best could explain the variation in bone loss. This is an interesting finding with respect to the controversial opinions about JANUARY
1988
VOLUME
59
NUMBER
1
BONE RESORPTION
AROUND
FIXTURES
the relative etiologic importance of plaque and trauma from occlusion in periodontal disease.23~26 The varying reactions around fixtures of different locations should be studied further. From a clinical point of view the most distal fixtures in patients with cantilever prostheses have usually been assumed to be exposed to the most risk. This does not appear to be so with respect to bone loss, according to the present results. The patients of this study will be reviewed for additional analyses. SUMMARY
11.
12.
13.
14.
Bone loss around osseointegrated titanium fixtures supporting mandibular fixed prostheses has been measured by means of stereoscopic intraoral radiography. Forty-six patients treated with the osseointegration implant method according to Branemark have been followed for an observation period of up to 6 years. The bone loss was s~mall,approximately 0.5 mm during the first postsurgical year and thereafter 0.06 to 0.08 mm annually. Poor oral hygiene and clenching of teeth significantly influenced bone loss. More bone was lost around the medial fixtures than around the more posterior ones.
15.
16.
17.
18.
19.
REFERENCES 1. Atwood DA. Reduction of residual ridges: a major oral disease entity. J P~OSTHETDENT 1971;26:266-79. 2. Carlsson GE, Bergman B, Hedcgard B. Changes in contour of the maxillary alveolar process under immediate dentures. A longitudinal clinical and x-ray cephalometric study covering 5 years. Acta Odontol Stand 1967;25:1-31. 3. Carlsson GE, Persson G. Morphologic changes of the mandible after extraction and wearing of dentures. Odont Revy 1967; 1827-54. 4. Tallgren A. Continuing reduction of residual alveolar ridges in complete denture wearers: mixed longitudinal study covering 25 years. J F'RCLSTHET DENT 1972;27:120-32. Bergman B, Carlsson GE. Clinical long-term study of complete denture wearers. J F'RCXTHETDENT 1985;53:56-61. Zarb GA. The edentulous milieu. J PROSTHET DENT 1983; 49825-31. Lindquist L, Carlsson GE, Hedegard B. Changes in bite force and chewing efficiency after denture treatment in edentulous patients with denture adaptation difficuhics. J Oral Rehabil 1986;13:23-29. 8. Tuncay OC, Thomson S, Abadi B, Ettinger C. Cephalometric evaluation of the changes in patients wearing complete dentures. a ten-year longitudinal study. J F'ROSTHETDWT 1984;51:16980. 9. Brinemark P-I, Zarb GA, Albrektsson T. Tissue-integrated
THE JOURNAL
10.
OF PROSTHEI’IC
DRNTISTRY
20. 21.
22.
23. 24.
25.
26.
prosthesis-osseointegration in clinical dentistry. Chicago: Quintessena Pub1 Co Inc, 1985. Br&mark P-I. Osseointegration and its experimental background. J &LkWIiET DENT 1983;50:399-410. HaraIdson T, Carlsson GE, IngervaII G. Functional state, bite force and postural muscIe activity in patients with osseointegrated oral implant bridges. Acta Odontol Stand 1979;37:195-206. Haraldson T. Functional evaluation of bridges on osseointegrated implants in the cdentulous jaw [Thesis]. Faculty of Odontology, University of Giiteborg, Sweden, 1979. Adell R, Lekhohn U, Rockier B, Branemark P-I. A 15-year study of osseointegrated implants in the treatment of the edentulous jaw. Int Oral Surg 1981;10:387-416. Adell R. Long-term treatment results. In: Brslemark P-I, Zarb GA, Albrektsson T, eds. Tissue-integrated prostheses. Osscointegration in clinical dentistry. Chicago: Quintessence Pub1 Co Inc, 1985;175-86. Lindquist LW Carlsson GE. Long-term effects on chewing with mandibular fixed prostheses on osseointegrated implants. Acta Odontol Stand 1985;43:39-45. Lindquist LW, Carlsson GE, GIanta P-O. Rehabilitation of the edentulous mandible with a tissue-integrated fixed prosthesis: a six-year longitudinal study. Quintessence Int 1987;18:89-96. Hollender L, Rockier B. Radiographic evaluation of osseointegrated implants of the jaws. Dento-Maxillo-Fat Radio1 1980; 9:91-s. Strid K-G. Radiographic results. In: Branemark P-I, Zarb GA, Albrektsson T, eds. Tissue-integrated prostheses. Osseointcgration in clinical dentistry. Chicago: Quintessence Pub1 Co Inc, 1985;317-27. Bradley JV. Distribution-free statistical tests. New Jersey: Prentice Hall Inc, 1968. Siegel S. Non-parametric statistics for the behavioural sciences. Tokyo: McGraw-Hill Book Co Inc, 1956. Adell R, Lekholm U, Rockier B, B&cmark P-I, Lindhe J, Eriksson B, Sbonrdone L. Marginal tissue reactions at osseointegrated titanium fixtures. I. A 3-year longitudinal prospective study. Int J Oral Maxillofac Surg 1986;15:39-52. Lekholm U, Adell R, Lindhe J, Branemark P-I, Eriksson B, Rockier B, Lindvall A-M, Yoneyama T. Marginal tissue rcactions at osseointegrated titanium fixtures. II. A cross-sectional retrospective study. Int J Oral Maxillofac Surg 1986;15:53-6. Lindhe J. Periodontology. Copenhagen: Munksgaard, 1983. Zarb GA, Symington JM. Osseointegrated dental implants: preliminary report on a replication study. J PROSI-HETDENT 1983;50:271-6. Lundqvist S, Carlsson GE. Maxillary fixed prostheses on osseointegrated dental implants. J PROSMET DENT 1983;50:26270. Ramfprd SP, Ash MM. Periodontology and periodontics. Philadelphia: WB Saunders Co, 1979.
Reprint requeststo: Da. L&s LINLQJIST ~GSLYCKAN 25 S-427 00 BILLDAL SWEDEN
63
PROSTHETICS
. DENTAL IMPLANTS
SECTIONEDIT0R.S I. KENNETH
,4DISMAN
RONALD
P. DESJARDINS
Bone resorption around fixtures in edentulous patients treated with mandibular fixed tissue-integrated prostheses Lars W. Lindquist, D.D.S.,* Birger Rockier, D.D.S.,** Gunnar E. Carlsson, D.D.S., Odont.Dr.*** University
of G8teborg,
Faculty
of Odontology,
Gijteborg,
Sweden
T
he gradual reduction of edentulous residual alveolar bone supporting complete dentures is a major oral disease entity.’ Several longitudinal studies have indicated that morphologic changes of denture-bearing regions are inevitable even if they show great individual variation.2-5 Changes of the prosthesis support, especially in the mandible, may compromise denture wearing and masticatory functions. 6,7The amount of bone reduction is generally greater in the mandible, which implies that the mandibular denture usually poses greater clinical problems for the patient and the prosthodontist.* The successful replacement of lost natural teeth by tissueintegrated dental implants is therefore an exciting improvement in clinical dentistry.9 The experimental background and the biologic and functional successwith fixed prostheses on osseointegrated implants have been well documented.‘O-‘5 Of particular interest is the reaction of the bone after implant therapy. The fixed prosthesis on osseointegrated implants provides a different type of stimulation to the bone that a conventional denture. It has been reported9 than the mean annual “marginal bone loss” around osseointegrated fixtures is at most 0.1 mm, which is substantially less than that under conventional dentures.lV5 This article analyses bone resorption around fixtures in association with treatment of the edentulous mandible with fixed prosthesis on tissue-integrated implants.
MATERIAL
AND METHODS
Forty-six patients comprising two groups of patients, 25 and 21 persons (Table I), were treated with mandibular fixed prostheses on tissue-integrated implants (TIPS) according to principles described elsewhere.9s’6 All treatment was performed by the same prosthodontist and the laboratory work was done by the same dental technician throughout the period of investigation. After TIP treatment the first group of patients (group 1) has *Chief, Clinic of Prosthodontics, Community Dental Health Service, GGtehorg, Sweden. **Assistant Professor, Department of Oral Radiology. ***Professor and Chairman, Department of Prosthetic Dentistry. THE JOURNAL
OF PROSTHETIC
DENTISTRY
and
Table I. Age and sex distribution
of the two patient groups at the final follow-up Age Group 1
2
Sex
-40
41-50
51-a
61-65
F M
2 1
3 2
11
3 1
F
2
M
1
2 2
10 1
2
Total
3
19 6 25 17
-
a
21
been observed for 5% to 6 years and group 2 for approximately 3 to 4 years. The patients were originally selected for the two matched groups with respect to age, sex, and degree of mandibular resorption.’ All of the patients received the same type of treatment and the only difference between the groups was the length of the follow-up period.
Radiographic examination
and measurements
A stereoscopic radiographic technique has been used according to principles described previously.“,‘* The radiographic examination was routinely performed 1 week after the abutment operation, 6 and 12 months postoperatively, and once every 12 months thereafter. The original, l- and 3-year and final intraoral radiographs were used in this study. The radiographs were inspected with respect to bone loss and change of density and architecture of the bone around the fixtures. The “marginal bone height” (height of the bone anchorage zone, Fig. 1) of each fixture was measured mesially and distally by using the fixture threads as an internal dimensional reference. Each thread is 0.6 mm, but it can distinctly be divided into halfs; thus the measuring unit used was 0.3 mm. The means of the mesial and distal measurements have been used as a value for each fixture.
Other variables Clinical recordings of bite force, chewing efficiency and other masticatory parameters, anamnestic and clini59
LINDQUIST,
ROCKLER,
AND
CARLSSON
0.5 -
1.0 -
0A
0B Fig. 1. Measurement of height of bone anchorage (marginal bone height). Mean of mesial and distal values (M[h, + hJ) was used for each fixture. cal dysfunction indices, attrition and occlusal wear, and degree of bone resorption before TIP treatment (from profile radiographs) were performed according to methods and principles described previously.‘, 15*l6 Oral hygiene was assessedretrospectively from scrutiny of the record of each patient. At each visit during the observation period the oral hygiene level was evaluated according to a 3-point scale: 0 = no visible plaque; 1 = local plaque accumulation (<25% of the visible abutment area); and 2 = general plaque accumulation (>25%). An oral hygiene index was calculated by adding the scores and dividing by the number of visits. The index could thus have values between 0 and 2. The extension of the cantilever part of the prosthesis was measured in millimeters from the distal surface of the most posterior fixture on each side.
Statistical method Significance tests for differences between groups were performed with Pitman’s permutation test.19For correlation analysis the nonparametric Spearman rank correlation test was used.20
RESULTS None of the 276 fixtures was lost during the observation period. The density of the bone around the fixtures seemedin general to increase indicating osseointegration. 60
MM
-0
GROUP
1
-v-Q
GROUP
2
RESORPTION
Fig. 2. Mean values of bone loss around all fixtures in 25 patients followed up for 6 years (group 1) and 21 patients for 3 years (group 2) after treatment with mandibular fixed prosthesis on tissue-integrated implants. The bone loss around the fixtures during the first 3 years after treatment was similar for the two groups (Fig. 2). The greatest loss occurred during the first year (0.40 to 0.45 mm), after which the annual resorption was 0.07 to 0.08 mm. During the next 3 years, group 1 showed a reduction of the bone height of even less magnitude: the mean annual loss for all fixtures from 3 to 6 years was
0.06 mm. The marginal bone loss differed among the various fixtures. The medial fixtures had more bone loss than the posterior ones (Fig. 3). This was a consistent finding in bone groups and it was evident after 1 year. Analysis of various factors influencing the bone loss was performed by dividing the material into subgroups and by correlation tests. Oral hygiene influenced the degree of bone resorption: patients with poor oral hygiene had more bone loss than those with no remarks of their hygiene (Fig. 4). The length of the cantilever extensions tended to be of increasing importance with time for the bone loss of the medial fixtures; after 6 years, seven patients with long cantilevers bilaterally (L 15 mm) had a mean loss around the medial fixtures of 0.95 mm whereas six patients with short cantilevers (<15 mm) had 0.61 mm. The differences for the more posterior fixtures were nonsignificant. The same tendency, not reaching a statistically significant level, was seen in group 2 with a shorter observation period.
Correlations The bone loss around the fixtures was tested for correlation to a series of recorded factors. The variable most strongly correlated to bone loss in group 1 was poor oral hygiene (Table II). This finding was also verified in group 2. Functional recordings such as bite force, chewing efficiency and other registrations related to mastication, and anamnestic and clinical dysfunction JANUARY
1988
VOLUME
59
NUMBER
1
BONE RESORPTION
AROUND
FIXTURES
GROUP I RESORPTION
13
6
6
13
13
6
13
Rl
R2
R3
6
6
13 L2
Ll
13
6 L3
YEARS LOCATION
GROUP II RESORPTION MM
0.5
0B
1
3 R3
1
3 R2
1
3
13
Rl
Fig. 3. Mean values of bone loss around length of observation period.
indices were not significantly
correlated
to bone loss.
Reported tooth clenching and recorded occlusal wear on the prostheses showed relatively strong correlations to bone loss that were significant for single calculations (Table II). The pretreatment degree of mandibular resorption was not significantly correlated to the bone loss around the fixtures. The length of the cantilever extension of the fixed TIP was not significantly correlated to bone loss around the fixtures for any of the parameters included in Table II. The continuing bone loss around some of the fixtures (R2, Vl , V3) from 3 to 6 years in group 1 was positively correlated (p < 0.05) to the length of the cantilever extensions and this was verified for the mean bone loss for all fixtures during 3 to 6 years. In group 2 the correlations were similar but usually they did not reach a statistically significant level.
Ll
1
13
3
YEARS
L3
LOCATION
separate fixtures
according
L2
to location
and
ORAL
RESORPTION
HYGIENE
GOOD
MM
POOR I
1
3
6
YEARS
Fig. 4. Mean bone loss around all fixtures in nine patients with good oral hygiene (no remark of plaque at recall visits during observation period) and nine
patients with poor oral hygiene (frequent remarks of plaque accumulation).
Multivariate
analysis
Multiple stepwise regression analyses were performed with some mean values of bone resorption (0 to 3 years, 0 to 1 year, and 1 year to the final visit) as dependent variables and the following 12 independent variables: THE JOURNAL
OF PROSTHETIC
DENTISTRY
original bone resorption level, oral hygiene, reported clenching of teeth, tooth wear, mucosal ridging, maximal bite force and finger force, bite force as in chewing and forceful biting, mean length of cantilever extensions, and 61
LINDQUIST,
ROCKLER,
AND
CARLSSON
Table II. Spearman rank correlation coefficients between marginal bone loss around osseointegrated fixtures during a 6-year period after treatment and three other factors in 25 patients with mandibular fixed TIP Years O-6
Oral hygiene Occlusal wear Tooth clenching
R3
RZ
Rl
Ll
L2
0.15 0.46’ 0.11
0.44* 0.35 0.41
0.52t 0.05 0.38
0.52t 0.08 0.33
0.53t 0.28 0.34
o-1
o-3
L3
x
x
0.53t 0.26 0.29
0.42’ 0.19 0.27
o.sot 0.32 0.41*
83 and L3 are the most posterior right and left fixtures, Rl and Ll are the most anterior. l 0.01 < p < 0.05. fo.001 < p < .Ol.
Table III. A stepwise multiple
regression
analysis with mean bone loss around mandibular fixtures as dependent variable in 46 TIP patients Variables
Dependent
Independent
F value
R’
A
Oral hygiene Clenching of teeth Mucosal ridgings Clenching of teeth Oral hygiene Oral hygiene Length of cantilever extension
16.3 7.3 2.2 12.5 4.5 5.0 3.4
0.27 0.38 0.41 0.24 0.32 0.11 0.18
B C
A = 0 to 3 years; B = 0 to 1 year; C = 1 year to final visit.
anamnestic and clinical dysfunction index values. In the analysis in both groups taken together, oral hygiene and clenching of teeth were the most strongly correlated independent variables for the first observation periods (Table III). Oral hygiene was also the first independent variable to enter the equation in an analysis with the mean bone loss from the l-year to the final recall visit, and the mean length of the cantilever extension showed the only further significant correlation with that dependent variable (Table III, C’). Similar results were found in separate analyses in the two groups. In addition to the significant variables shown in Table III, bite force values also reached a significant level of correlation with the dependent variables in single analyses in the separate groups.
DISCUSSION The continuous and inevitable bone resorption associated with conventional removable dentures should be contrasted with the results of this study. The most remarkable finding is therefore the extremely small amount of bone resorption that occurred during the first 62
6 years after treatment with fixed tissue-integrated prostheses in previously edentulous mandibles. That no single fixture was lost during the observation period also deserves to be emphasized. ,These results give further evidence of the favorable biologic results this therapy seems to offer.6-16The bone loss in this study is even smaller than reported previously for the first year after prosthesis connection and later.13 This might be explained by the fact that the surgical and prosthetic methods have been refined since the first developmental period, as corroborated in recent reports.21s22The longterm development for osseointegrated fixtures thus appears to be extremely good. With less than 0.1 mm bone loss per year after the postsurgical period, the prognosis for life-long function is evident for most tissue-integrated implants. Oral hygiene was found to be the most important factor associated with marginal bone loss. This finding is not surprising with respect to current periodontal concepts.23 However, the reactions in the marginal soft tissues and the microbiota in the perifixtural pockets seem to differ from those around natural teeth. The soft tissue-titanium relationship perhaps should not be assessed by conventional indices.21,22p24The careful instructions in oral hygiene recommended for TIP patients to avoid compromises in gingival health seem to be necessary also to minimize the bone loss around the fixtures.9s25 According to the analyses, functional and loading factors were also of importance. Parafunctional activity such as bruxism, both as reported tooth clenching and recording of occlusal wear on the prosthesis, led to increased bone loss. The correlation between the length of the cantilever extensions and bite force on one side and some bone loss values on the other side also indicated possible influences of overloading. The multivariate analysis verified that a combination of poor oral hygiene and extensive loading were the factors that best could explain the variation in bone loss. This is an interesting finding with respect to the controversial opinions about JANUARY
1988
VOLUME
59
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BONE RESORPTION
AROUND
FIXTURES
the relative etiologic importance of plaque and trauma from occlusion in periodontal disease.23~26 The varying reactions around fixtures of different locations should be studied further. From a clinical point of view the most distal fixtures in patients with cantilever prostheses have usually been assumed to be exposed to the most risk. This does not appear to be so with respect to bone loss, according to the present results. The patients of this study will be reviewed for additional analyses. SUMMARY
11.
12.
13.
14.
Bone loss around osseointegrated titanium fixtures supporting mandibular fixed prostheses has been measured by means of stereoscopic intraoral radiography. Forty-six patients treated with the osseointegration implant method according to Branemark have been followed for an observation period of up to 6 years. The bone loss was s~mall,approximately 0.5 mm during the first postsurgical year and thereafter 0.06 to 0.08 mm annually. Poor oral hygiene and clenching of teeth significantly influenced bone loss. More bone was lost around the medial fixtures than around the more posterior ones.
15.
16.
17.
18.
19.
REFERENCES 1. Atwood DA. Reduction of residual ridges: a major oral disease entity. J P~OSTHETDENT 1971;26:266-79. 2. Carlsson GE, Bergman B, Hedcgard B. Changes in contour of the maxillary alveolar process under immediate dentures. A longitudinal clinical and x-ray cephalometric study covering 5 years. Acta Odontol Stand 1967;25:1-31. 3. Carlsson GE, Persson G. Morphologic changes of the mandible after extraction and wearing of dentures. Odont Revy 1967; 1827-54. 4. Tallgren A. Continuing reduction of residual alveolar ridges in complete denture wearers: mixed longitudinal study covering 25 years. J F'RCLSTHET DENT 1972;27:120-32. Bergman B, Carlsson GE. Clinical long-term study of complete denture wearers. J F'RCXTHETDENT 1985;53:56-61. Zarb GA. The edentulous milieu. J PROSTHET DENT 1983; 49825-31. Lindquist L, Carlsson GE, Hedegard B. Changes in bite force and chewing efficiency after denture treatment in edentulous patients with denture adaptation difficuhics. J Oral Rehabil 1986;13:23-29. 8. Tuncay OC, Thomson S, Abadi B, Ettinger C. Cephalometric evaluation of the changes in patients wearing complete dentures. a ten-year longitudinal study. J F'ROSTHETDWT 1984;51:16980. 9. Brinemark P-I, Zarb GA, Albrektsson T. Tissue-integrated
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prosthesis-osseointegration in clinical dentistry. Chicago: Quintessena Pub1 Co Inc, 1985. Br&mark P-I. Osseointegration and its experimental background. J &LkWIiET DENT 1983;50:399-410. HaraIdson T, Carlsson GE, IngervaII G. Functional state, bite force and postural muscIe activity in patients with osseointegrated oral implant bridges. Acta Odontol Stand 1979;37:195-206. Haraldson T. Functional evaluation of bridges on osseointegrated implants in the cdentulous jaw [Thesis]. Faculty of Odontology, University of Giiteborg, Sweden, 1979. Adell R, Lekhohn U, Rockier B, Branemark P-I. A 15-year study of osseointegrated implants in the treatment of the edentulous jaw. Int Oral Surg 1981;10:387-416. Adell R. Long-term treatment results. In: Brslemark P-I, Zarb GA, Albrektsson T, eds. Tissue-integrated prostheses. Osscointegration in clinical dentistry. Chicago: Quintessence Pub1 Co Inc, 1985;175-86. Lindquist LW Carlsson GE. Long-term effects on chewing with mandibular fixed prostheses on osseointegrated implants. Acta Odontol Stand 1985;43:39-45. Lindquist LW, Carlsson GE, GIanta P-O. Rehabilitation of the edentulous mandible with a tissue-integrated fixed prosthesis: a six-year longitudinal study. Quintessence Int 1987;18:89-96. Hollender L, Rockier B. Radiographic evaluation of osseointegrated implants of the jaws. Dento-Maxillo-Fat Radio1 1980; 9:91-s. Strid K-G. Radiographic results. In: Branemark P-I, Zarb GA, Albrektsson T, eds. Tissue-integrated prostheses. Osseointcgration in clinical dentistry. Chicago: Quintessence Pub1 Co Inc, 1985;317-27. Bradley JV. Distribution-free statistical tests. New Jersey: Prentice Hall Inc, 1968. Siegel S. Non-parametric statistics for the behavioural sciences. Tokyo: McGraw-Hill Book Co Inc, 1956. Adell R, Lekholm U, Rockier B, B&cmark P-I, Lindhe J, Eriksson B, Sbonrdone L. Marginal tissue reactions at osseointegrated titanium fixtures. I. A 3-year longitudinal prospective study. Int J Oral Maxillofac Surg 1986;15:39-52. Lekholm U, Adell R, Lindhe J, Branemark P-I, Eriksson B, Rockier B, Lindvall A-M, Yoneyama T. Marginal tissue rcactions at osseointegrated titanium fixtures. II. A cross-sectional retrospective study. Int J Oral Maxillofac Surg 1986;15:53-6. Lindhe J. Periodontology. Copenhagen: Munksgaard, 1983. Zarb GA, Symington JM. Osseointegrated dental implants: preliminary report on a replication study. J PROSI-HETDENT 1983;50:271-6. Lundqvist S, Carlsson GE. Maxillary fixed prostheses on osseointegrated dental implants. J PROSMET DENT 1983;50:26270. Ramfprd SP, Ash MM. Periodontology and periodontics. Philadelphia: WB Saunders Co, 1979.
Reprint requeststo: Da. L&s LINLQJIST ~GSLYCKAN 25 S-427 00 BILLDAL SWEDEN
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