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Prosthetic aspects of osseointegrated fixtures supporting overdentures. A 4-year report
Prosthetic aspects of osseointegrated overdentures. A 4-year report I. Naert, D.D.S.,* M. Quirynen, G. Theuniers, D.D.S., Ph.D.,***
D.D.S., Ph.D.,** and D. van Steenberghe,
fixtures
supporti,ng
M.D., Ph.D.****
Catholic University of Leuven, Leuven, Belgium Eighty-six consecutive patients, provided with 84 resilient and two nonresilient overdentures (six in the upper and 80 in the lower jaw), were examined. The overdentures were supported by a total of 173 osseointegrated titanium fixtures (the standard Branemark abutment), with a mean loading time of 19.1 months (range 4 to 48 months). In each jaw only two fixtures anchored the overdentures. No failures occurred during the observation period but two fixtures were lost before loading. The radiographic annual bone loss around fixtures in the lower jaw was -0.8 mm for the first year and less than -0.1 mm for the following years. The change in marginal bone height did not correlate with parameters such as the occlusion and articulation pattern, the presence or absence of a soft liner around the abutments, and the magnitude of the interabutment distance. The patients’ reactions to overdenture treatment were, on the whole, positive concerning chewing function, phonetics, and comfort. The need for maintenance care of the clip-bar attachment was minimal. (J PROSTAET DENT 1991;65:071-80.)
W
hile many edentulouspatients are satisfiedwith a complete denture rehabilitation to restore oral function and cosmetics,others suffer from this kind of treatment.’ The problems encountered are either functional or psychosocial,or both. Reduction of stability, retention, and load-bearing capacity have beenconsideredmajor factors for this compromised oral function. Psychosocially, patients suffer becauseof a constant fear of dentures loosening during jaw movements. Those patients who wear removable dentures do not usually seek the replacement of their unstable complete denture by a fixed prosthesis.They are pleasedwhen provided with a stable denture at limited financial expense. The functional benefitsof complete denturessupported by the retention of a few roots have been clinically documented.z It is tempting therefore to adapt the osseointegration method to the overdenture concept in patients who can accept wearing removable dentures. Preliminary results3V5 indicate the functional benefits of this technique. In addition, the overdenture concept can behelpful in some clinical situations, such as severely resorbedjaws with unfavorable jaw relations where maximal soft tissue support is required to enhancethe cosmetic and phonetic results.
*Lecturer, Department of Prosthetic Dentistry. **Professor, Department of Periodontology. ***Professor, Department of Prosthetic Dentistry. ****Professor and Head, Department of Periodontology. 10/1/262t36
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Although someof the clinical data6obtained from patients with fixed prosthesescan be extrapolated to the overdenture situation, the important clinical differences imposed the need for prolonged observation periods. This study evaluated the 4-year experience with overdenture therapy from a prosthetic point of view. The periodontal aspectsare dealt with in a companion article.7
MATERIAL From November 1984to May 1988,two or three fixtures (Branemark implants are commonly called fixtures) were installed in one or both jaws of 86 consecutivepatients. In six patients the fixtures were localized in the maxillae and in 80 patients they were localized in the mandible. Approximately three times more women (65) than men (21) were treated. The youngest patient was 33 years of age, while the oldest was77 years of age (meanage 56.5). A total of 196 Branemark implants were monitored (Nobelpharma AB, Gothenburg, Sweden). In eachmandible, two fixtures were installed in the symphysealregion, mostly in the canine region, with a connecting line parallel to the terminal mandibular hinge axis.5 A third fixture was installed in the vicinity of the midline when overdenture therapy wasbegun in our center to act asa reserve in case one of the other two fixtures would fail. Until now all but two of these third fixtures (n = 21) have remained “sleeping.” In one patient the “sleeping” fixture appeared supragingivally 1 week after the abutment connection of the other two fixtures. In this patient, the three fixtures and magnetswere usedas an attachment system. In the other
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NAERT ET AL
I. Frequency distribution of length of loaded fixtures (N = 173) by jaw Table
No. of loaded Fixture length (mm)
Mandible
7 13 15 18 20
1. To reinforce resin base, a chrome-cobalt alloy framework was used, to which the retention clip was soldered. Fig.
0 1
0 0
Table II. Mean time of edentulousnessand number of complete dentures worn Number
O-5 y 6-15 y 16-34 y
672
0 11
before loading.
Edentulousness (n = 8.6 yr)
patient, the “sleeping” fixture wasusedbecauseof the anticipated nonintegration of the neighboring fixture (buccal dehiscenceand lingual fenestration) at the fixture installation. In the maxillae, two fixtures were installed in the canine-first premolar region. The frequency distribution and the length of the fixtures in eachjaw are presentedin Table I. The quality and resorption of the jawswere evaluated by the surgeonat fixture installation by assessing the preoperative radiographs, according to the Lekholm and Zarb classification.* Both the bone quality and quantity were noted for eachjaw. The meanquality wasmoderatefor the maxillae, Ti = 2.5 (range 1to 4) and mandible,g = 2.2 (range 1 to 4). The mean resorption anatomy wassevere for the maxillae, ii = 4.6 (range 3 to 5) and moderatefor the mandible, ‘ji = 2.4 (range 1 to 5). Most patients had an Angle classI jaw relationship (82% ), while the remaining patients were evenly distributed between classesII and III. The status of the antagonist jaw was edentulous (82% or dentate (15%); in 3% an osseointegrationfull fixed partial denture waspresent. The meantime of edentulousnesswas 8.6 years (range 0 to 34) and the average number of worn complete dentures was 2 (range 9 to 6) (Table II). Functional problemswerethe main reasonfor consultation in three quarters of the patients. These patients complained of lack of retention or stability with the existing dentureswhile eating or talking. The othershad psychosocial problems with fear of loose dentures. They would, however, accept removable dentures when retention was assured. The reason why the patients chose the overdenture therapy instead of a tissue-integrated fixed partial denture wasthe needto increasethe stability and retention of the complete denture (Table III). Another group of patients chosethe overdentures becauseof limited financial resources.Indeed, neither implants nor fixed prothesesare
Maxillae
4 47 (l)* 55 46 (l)* 6 3
10
*Lost fixture
fixtures
39%
38%
23%
0
1
of dentures (rn=2) 2
3
16% 24% 30%
15%
4
z-5
10% 5%
reimbursedby the Belgian Social Security system.In 12% of the patients, an overdenture wasmade instead of a tissue-integrated fixed partial denture becausethe patients were unable to choosefor themselves. The meanloading times for the fixtures in the mandible and maxillae were 19.7 months (range 4 to 48) and 11.7 months (range 4 to 28), respectively. The distribution of installed overdentures by year is given in Table IV. In 78 patients, in the mandible, egg-shapedDolder type bars (No. 53.01-2, Cendres et Metaux SA, Biel, Switzerland) screwedonto two fixtures were usedas an attachment system. The height of the abutment at the time of impression fabrication was 1 mm to a maximum 2 mm above the gingiva. This favored an optimal plaque control maintenance regimen and minimal leverage. A spacemaintainer 0.75 mm thick wasplacedbetweenthe bar and the retention clip before processing,and all overdentures with this retention system were reinforced by a chrome-cobalt alloy framework (Fig. 1). Approximately half of the overdentureswere processedwith a soft liner (Supersoft, Coe Laboratories Inc., Chicago,Ill.) around the bar and gold cylinders on top of the abutments. This procedurewasfollowed to lower the open spaceunderneath the overdentures, preventing food impaction and soft tissueproliferation. Supersoft liner was chosenbecauseof its goodbinding capacity to acrylic resin. Furthermore, in two patients, Rare Earth Jacksonmagnets (Solid State Inc., Mount Airy, NC.) were used. In the maxillae of one patient, a round curved bar connectedthe fixtures to a molar on both sides,thus achieving a nonresilient design.In four patients, O-rings (NobelpharmaAB) were used,and in one patient Rare Earth Jacksonmagnets were usedin the maxillae.
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OVERDENTURE
THERAPY
GAIN
Table III. Patient’s reason for choosing overdenture therapy instead of tissue-integrated prosthesis
+0.5
Reason
Frequency (TO)
Only need for increased stability
40
and retention Financial Extreme bone resorption Wanted unfixed rehabilitation Unfavorable jaw relation Advised by dentist Only advised on overdenture
mean C M 6 Ii
36 5 1 1
-1.0
1985
1986
1987
1988
1989
9
2 10
-
3
1
24
34
3
METHODS All parameterswere registeredat the time of placement of the overdentures, 1 to 2 weekslater, and from then on every 6 months up to the end of the observation period (4 to 48 months). The following prosthetic parameters were considered: (1) occlusion and articulation, (2) prosthesis stability and retention, (3) the need for relining, (4) complications of the implant components, and (5) denture materials. All complications that occurred in between the recall visits were also registered. Between November 1988and April 1989,all 866patients had a final clinical and radiographic examination by the sameperiodontist (MQ) and prosthodontist (IN). Six of the 86 patients did not return for this control visit; three had moved abroad, and the others preferred to remain with their own dentist for control assessment. Thesecolleagues
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All overdentures were carefully checked for balanced occlusionon the articulator and intraorally without anterior tooth contacts in the centric relation. The interocclusal spaceranged from 2 to 3 mm as measuredbetween reference points on the nose and on the chin.g The retention clips were adjusted during installation of the overdenture sothat during extreme opening of the mouth and with vigorous tongue movement the prosthesiswould not be dislodged. The interabutment distance in the mandible ranged from 8 to 29 mm (mean20 mm). In the maxillae, the interabutment distancerangedfrom 24to 39 mm (mean32 mm) measuredalongthe ridge and not alongthe connectingline. Only one fifth of the patients had not worn a transitional prosthesisbetween the fixture installation and the abutment connection.
THE
O-6 O
5 12
Table IV. Distribution (number of patients) of overdenture installation by year and by jaw
Maxillae Mandible
mm r
DENTISTRY
i
mm
LOSS.
Fig. 2. Mean change in marginal bone height for different periodsof fixture loading (number of fixtures involved).
discussedthe treatment results for these patients by telephone communication. The closebone apposition for eachfixture, after disconnecting the bars, wasevaluated clinically and radiographically. The mobility wasassessed by tapping the abutments alternatively back and forth with two instrument handles and by careful eye inspection of the bone-fixture interface on long-cone radiographs.From 1988onward, fixture mobility was also assessed by meansof the Periotest instrument (SiemonsAG, Bensheim, Germany).7*lo*r1 A fixture wasconsiderednonintegrated: first, if a free-standing fixture showedthe slightest sign of mobility; second,when a peri-implant radiolucency could be detected; and finally, if the fixture showedsignsor symptomsof pain or infection. Radiographs were made at the abutment connection with the parallel technique every 6 to 18 months.12The marginal bone height (MBH) was measured on these radiographs. The MBH was defined as the mean distance between the fixture-abutment junction and the marginal bone level mesially and distally from the fixture to the nearest0.3 mm.7This distancecorrespondsto half the distance between threads. Only those radiographswere used in which the fixture threads could easily be defined. All radiographs were examined by the sameinvestigator (MQ). Becausethe loading time ranged from 4 to 48 months and because consecutive radiographs ranged from 6 to 18 months, the data can differ for each time period. For the longitudinal evaluation, the periodical changein marginal bone height was calculated.’ The intermittent change in marginalbone height wascalculated and wasdefined asthe changein marginal bone height over a 6- to 12-month period, at two consecutiveappointments (0 to 6 months, 6 to 12 months, 12to 24 months, and 24to 36 months). Because
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mern c n 0 B Ii
24-30-36
24-30-36
HONTHS
24-30-36
ET AL
MONTHS
HONTHS
Fig. 3. Mean change in marginal bone height (CMBH) correlated with incisal contact (A), balanced articulation (B), interabutment distance (C), and soft liner (D) for different periods of function (number of fixtures involved).
Overdenture Frequency %
,
75
191 /
7
rl
I I &
O-b
b-12
12-18
18-Z&
2'+-30
30-36
36-42 MONTHS
Fig. 4. Frequency distribution of overdentures with soft liner (n = 42) where soft liner was still soft, by period.
of the limited number of observations in the maxillae, the change in marginal bone height could not be calculated. The gingival recession, defined as the distance from the top of the abutment to the gingival margin, was measured on six sites per abutment to the closest 0.5 mm. The hardness of the soft liner on the overdenture around
674
the abutments and bar was judged clinically. Incisal contact at centric occlusion and the articulation pattern, balanced or unbalanced, were also checked. The interocclusal space was clinically determined as the difference in distance of reference points on both the nose and chin at rest and at centric occlusion. The retentive force of each overdenture was judged by the same investigator (IN). The patient was asked to open his or her mouth as wide as possible, and to move the tongue outward. When the overdenture dislodged, a score of 0 was given. Furthermore, when the prosthesis was not loose the retention was judged by grasping the overdenture between index and thumb, above the bar, and an attempt was made to lift up the overdenture. If there was little or no resistance to move the overdenture, a score of 0 was given again. When resistance was felt, a score of 1 was given. At the final examination, the patients were asked for their reaction before and after the overdenture therapy and for their personal experience with their new overdenture. The answers for each question were given on a discontinuous analog scale with numbers ranging from 1 (very bad) to 9 (very good).
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cl
balanced
Overdenture Frequency %
balanced
became unbalanced
unbalanced
271
1
0 A
O-6
6-12
12-18
18-24
.30
24-30 MONTHS
1OC
no ~nclsal contact
0
Overdenture Frequency %
inw.1
contact
became
contact
became no contact
71 1.31
I101
\
i
O-6
6-12
12-18
18-Z&
IL
24-30
a30 MONTHS
5. Frequency distribution of overdentures with and without balanced articulation (A) and with and without incisal contact (B) and frequency of “changes” by period (number of overdentures). Fig.
RESULTS Fixture loss after
loading
During overdenture function (mean loading time: 19.7 [range 4 to 481, and 11.7 months[range 4 to 281 for the maxillae and mandible, respectively), no fixtures were either lost or showedsignsof symptomsof pain or infection. In one patient in whom a fixture had beenlost at the abutment installation, an overdenture anchored to one single fixture was designed5until a supplementary fixture was installed.
Change in marginal bone height to prosthetic parameters
in relation
The meanchangein marginal bone height for fixtures in the mandible, with egg-shapedbars asthe attachment system for different observation periods, is illustrated in Fig.
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2. For patients who had worn their overdentures for 6 months, a meanchangein marginal bone height of 0.5 mm wasobserved.For patients who had worn their overdenture for 1 year, a changein mandibular bone height of 0.75mm wasfound. During the secondyear of function, little or no changein marginal bone height could be detected (-0.01 mm). For the third year, on average,even a small“gain” of bone was observed (+0.12 mm). The change in marginal bone height wasalso analyzed in relation to the presence or absenceof incisal contact in centric occlusionand to the balancedor unbalancedarticulation at the beginningof the observation period. No correlation wasfound (Fig. 3, A and B). The interabutment distance and the use or nonuseof the soft liner in the overdenture around the retainer and abutments also played no significant role (Fig. 3, C and D).
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Overdenture Frequency
-
retentive
-
non-retentive
q q ’ ‘( ”
00.
0 times activated
0.0.
%
100
1211Total
Patient’s Frequency % (n-78)
0
before
m
after
ET AL
0.D O.D.
75
1201
50
25 l21Totrl
0 LL 6-12
12-24
24-48
MONTHS
Fig. 6. Periodical frequency distribution of retentive and nonretentive overdentures and number of times retention clips had been activated (number of overdentures).
0A
PCTSIV 100
Patient’s Frequency O/O
75
(n-78)
50
V. Changein interocclusal spaceby patient for different periods of overdenture wearing (number of patients) Table
Period
(mo)
O-6 6-12 12-18 18-24 24-30 30-36 36-42
+3.Smm
+2.5mm
2
+1.5mm
1
1
1
-
1
1 1
-
3 1 1
-
Soft liner properties gingival recession
-
and relation
0
15 4 5 5 6 2 3
1 1 2 1 1
to
The viscoelasticity of the soft liner material usedaround the retainer and abutments in the overdenture showeda decreasingcourse with time. In 66% of the overdentures provided with a soft liner (Fig. 4), the soft liner wasstill soft after 6 months of function;, this wasreduced to 40% after 1 year and to 8% after 2 years. The soft liner hasbeen renewed in only three patients sincethe overdenture installation. In patients wearing overdentures with soft liner around the abutments, the gingival recessionwasreduced by 60% compared with the recessionin those patients in whom no soft liner has been used.
Occlusibn,
articulation,
and vertical
height
Fig. 5 showsthe frequency distribution of overdentures with and without incisal contact, and with and without balancedocclusionfor different periodsof denture wearing. It also indicates the frequency of patients with a changed occlusal pattern at the start compared with the different evaluation periods. The group of patients that functioned with overdentures for more than 30 months showedan ar676
25
-1.5mm
0B
0I A CApN
A CApN
7. A: Frequency distribution of patients with negative subjective experiencewith their old denture and with their new overdenture. Questions asked of the patients (Yes/No response).Did you have pain or ulcerations with your old denture (P)? Did you have problemswhen chewing with your old denture (C)? Did you have problemswhen talking with your old denture (T)? Were your social contacts with others curbed becauseof your dentures (S)? Were you occupied all the time by your denture ($)? B: Frequency distribution of patients’ reactions to denture wearing before and after overdenture therapy. A, Always; C, only for chewing; Ap, only for appearance;N, never. Fig.
ticulation pattern that wasnot significantly different from that at the start. The observationsmade for the presence and absenceof incisal contact revealed a trend of losingincisal contact during the first year. For patients wearing overdentures for more than 18 months, more patients had incisal contact than those with suchcontact at the start of the study. The changein interoccusalspacefor individual patients at different periods of overdenture wearing is depicted in Table V. Sixty-eight percent of the patients had an unchangedinterocclusal spaceat these different periods.
Overdenture
retention
as a function
of time
Fig. 6 presents a histogram of the retentive and nonretentive bar-overdenture over different periods of function. All overdentures had a retention index of 1 at instal-
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Patlent’s
Patlent’s
%
% LO 1
40
301
30
20 -
Frequency
50
Frequency
&-A-1234567@)9
12
Patient’s
own apprcristlon
Patlent’s
own appratiatmn
3
4
5
6
1@9
Patent’s
own appreciation
Patient’s
own gprecirtmn
1234567@9
1236567@9
Patirnt’r Frequency %
56 -
1’
40-
30 -
20-
10 -
I
I
,234567@9 Patlent’s
own rpprcciatm
Fig. 8. Patients’ own appreciation of overdenture therapy on a scale of 1 to 9. 1 = Very bad; 9 = very good; 0 = median.
lation and after 1 or 2 weeks of function. The need for reactivation of retention clips or bars did not change appreciably in time. The clips were reactivated after 6 to 12 months of function in 3 of 23 patients, after 12 to 24 months in 4 of 21 patients, and after 24 to 48 months in 12 of 27 patients.
dian for these answers lies in score 8. Eighty percent of the patients answered positively regarding the question concerning the presence of food particles under the overdenture after meals. Sixty-five percent of them found this annoying.
Patients’
The complications during overdenture wearing are summarized in Table VI. The complications for the maxillary overdentures were related to the attachment systems. Bad experiences with the Jackson magnets required stopping their use. Corrosion and rapid loss of retention and extreme wear were the main reasons for this decision. O-ring box fracture occurred twice on eight O-rings, although they had been in place for only 5 months. The complications for the maxillary overdenture at the implant components are not reliable because of the limited number of treated patients. More important are the complications for the mandibular overdentures. Loose gold screws, the main complication at the implant component level, occurred in 5 % of the patients. Opposing complete denture fracture occurred in
reactions
Fig. 7 graphically depicts changes in negative subjective experiences and changes in denture wearing before and after overdenture installation. After overdenture installation, six patients still complained of pain when chewing. This pain was caused by pressure of the overdenture on the mental nerve or spiny residual ridges in very resorbed jaws. Psychologic problems persisted in two patients who asked for fixed prostheses where anatomic limitations precluded the installation of more than two fixtures. All patients except one always wore their overdentures. This same compliance pattern had only been 80% before overdenture therapy. The patients’ own appreciation on the whole scored very positive on the rating scales (Fig. 8). The me-
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Complications
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Table
VI.
Number of overdenture complications Maxillae
components (U:12/L:161) Abutment screwloose Goldscrewloose
Mandible
Implant
0
2
2 8 (5)
0
1
2
5 (100)
Overdenture parts
Reinforcingframeworkfracture (u:2/L:78) Corrosionand lossof retention of the Jacksonmagnets (l&2&5)
0 ring box fracture (US/L:O)
2
-
Opposing complete denture fracture -
(L:O/u:71) U, Upper jaw; L, lower jaw. Numbers in parentheses are percent
7 (10)
of cases.
10% of the patients. Even one overdenture chrome-cobalt alloy reinforcement fractured. Only six overdentures required relining. Treatment for gingival proliferation occurred in eight patients.
DISCUSSION The failure rate of loaded fixtures in this seriesof nongrafted and nonirradiated jawbonesrehabilitated by means of resilient overdentures is 0% over a 4- to 48-month period. Our failure rate after loading for the mandibular overdenture is in accordance with the less than 1% reported by other centers.4These data for the failure rate are only significant for the mandible. Becauseof the limited number involved in the present study, no conclusions can be drawn for the maxillae. Another restriction is the observation time, with an averageof 19.7months of function; this is far below the minimum of the 5 years requested.lOHowever, it isknown that if failures occur with Branemark implants, thesetake placeduring the healingor remodeling phase.l3 One could prudently extrapolate the present data to a long-term perspective, although this was only proved for implant-supported prostheses.14 The range and timing of bone level changesobservedapproachngthe zero line after 1 year are similar to those for fixtures supporting fixed prostheses,6p I53l6 which suggestsa favorable long-term prognosisfor overdentures in the mandible. The gain in meanbonelevel asobservedafter the second year is in agreementwith the results reported by Cox and Zarb.16A possibleexplanation is that in time bone remodeling occurs, resulting in the apposition of cortical bone, which becomesmore visible on radiographs.The difference observedover time wastoo consistentduring this period to be due to a measurementerror. The better results obtained for overdentures in the mandible when comparedwith complete fixed prostheses can be explained by the opportunity of selectinga site with optimal bonequality when only two fixtures have to be installed. The patient group in this study, contrary to that of 678
ET AL
the Swedishmulticenter study,4 did not consistof patients for whom it is anatomically impossibleto install more than two fixtures. On the contrary, in nearly all but five patients a fixed prosthesison four to six implants was a possible treatment alternative. Another reasonfor the excellent results wasthe overdenture designitself. By using only two fixtures with an interconnection parallel to the hinge axis, a resilient overdenture designis possible;this guarantees free rotation during dorsal loading, resulting in a twist-free load transmissionto the fixtures in a nearly axial direction. The absenceof anterior incisal contact in centric occlusionand the existenceof balancedarticulation in complete denture treatment have been advocated to favor the load distribution on the underlying supporting structures. The greater the interabutment distance, the greater are the loading forces on the fixtures. Absenceof anterior contact, presenceof balanced articulation, the use of a soft liner, and small interabutment distance contributed to the positive fixture-bone interface. However, the relationship between the change in marginal bone height and these mentioned factors could not be sustained. It should be mentionedthat the data werecross-sectionalin nature and thus the interindividual differences could have masked possiblelessimportant relationships.However, becauseof the high number of subjectsper observation, this risk was minimized. Therefore it is concludedthat the four abovementioned factors do not correlate with the change in marginal bone height for this period of observation. Proliferation of the gingiva around overdenture abutments, whether natural teeth or titanium implants, is a well-known fact.2p4 In the Swedishmulticenter study,4 hyperplasiatreatment occurred in 25% of the patient group. However, in this study only a few patients were observed, and this happened in the earlier treatment period. In patients in whom movable oral mucosasurroundedthe abutments, a gingival graft was performed around three abutments. This graft was only partially successfulin coping with the gingival overgrowth. An attempt to fill the dead spacearound the abutments with a soft liner did not fulfill the objectives either. Indeed, less gingival recessionwas observedwhen a soft liner was applied. Stringent oral hygiene and a nontraumatic overdenture designfor the soft tissueswill maintain healthy soft tissues.The premature insertion of the overdenture after the abutment connection also seemsto favor hyperplasia of the gingiva. A wait of some weeksto allow sufficient soft tissuehealing is recommended. After 1 year, soft liners harden in two thirds of the patients. The soft liner should be renewedat least every year if viscoelasticproperties are to be maintained.17It may be questionableto usea soft liner in the overdenture for the previously stated goal. IncisaI contact and articulation pattern may not be stable over time. However, checking incisal contact in centric occlusion showed changesover time. It should be rememberedthat 82% of the patients had a completedenture in the oppositejaw, which doesnot
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favor stability in recording. The incisal and articulation pattern were always registered at the overdenture installation and not after 1 or 2 weeks of function, the period of time needed for complete denture settling. In contrast to occlusion and articulation, the mean interocclusal space remained constant over the entire follow-up period. This fact does not contradict the previous assumption concerning difficulties of monitoring the denture position with precision after many months. Indeed, the interocclusal space relates to physiologic parameters such as muscle tonus and can adapt in time.g After the bar-attached overdentures had been functioning for 2 to 4 years, 72% of the overdentures were properly retained. Of the 71 bar-attached overdentures observed, five were in need of maintenance more than twice. The bar concept involves more effort from the dentist and the technician than the use of magnets, O-rings, or other nonsplinted abutment attachment systems. The long-term maintenance of the bar concept is only restricted by the activation of the retention clip. The manufacturers of the clip attachments should be stimulated to provide a device by which one could objectively quantify the retentive force of the clips, thereby preventing overactivation of the clip, which could lead to long-term harmful effects of the implant components or even to the fixture-bone interface. The patients’ own appreciation of the overdenture was, as in other studies,4 positive. Ninety-seven percent found the overdenture better than the previous denture, and about 95% never or only once daily removed their overdenture due to discomfort. Before treatment, 60% of the patients used denture adhesives, while none did so after overdenture treatment. Although the patients were satisfied with their overdentures, about one fourth of them would choose a fixed prosthesis over an overdenture if the treatment had to be repeated and/or when costs were not a hindrance. Patient selection should be considered carefully when an overdenture with a resilient design is advised instead of a fixed partial denture. Overdentures should be contraindicated (1) when patients with a favorable anatomy and jaw relations ask for a fixed prosthesis; (2) in patients who show advanced resorption in the mandible, with sharp, spiny ridges, and where the foramina mentales are superficially localized; (3) in patients who cannot accept the conditions that food impaction occurs under the overdenture and that the overdenture should be cleaned after meals-it may not be possible to lift up the overdenture with the tongue to sweep away food particles; and (4) when none of these criteria are met but when the patients cannot accept wearing removable dentures for psychologic reasons. The overall material drawbacks of bar-attached overdentures in the mandible were, apart from the use of a soft liner and its hardening, limited to one fracture of the Cr-Co reinforcement. This fracture presumes that bite force levels with overdentures are considerable. An increased number of midline fractures of conventional max-
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illary dentures after osseointegrated prosthetic treatment was also reported.ls Only six patients needed a relining of the overdenture base. Tilting and shifting forces, which are known to be the most detrimental for bone resorption, are rarely present in the bar-attached overdenture concept. A delayed bone resorption can be expected when compared with bone resorption under a complete denture. Moreover, more patients complained about less retentive maxillary complete dentures. Improved comfort with mandibular overdentures1g might be an explanation of the fact that patients unconsciously tend to compare the maxillary denture with the well-retained mandibular denture. Whereas no adverse tissue reactions were found when magnets were applied, it seems that with the use of O-rings, rapid bone loss around the fixtures occurs, at least in the maxillae.7 Because of the limited number of patients treated with magnets and O-rings, no conclusions can be made. Follow-up studies where fixtures are interconnected and not interconnected, and where different attachment systems are in use are presently in progress.
CONCLUSIONS From the observations made in this study, the following preliminary conclusions can be formulated. 1. Osseointegrated oral implants can be used with low failure rates, at least over a medium-term period, for resilient overdenture therapy in the mandible. Not a single failure occurred for bar-attached overdentures retained by a bar on two fixtures in the mandible when grafted and irradiated jaws were excluded. 2. The overdenture approach seems to be useful in patients who accept removable dentures, but who are handicapped because of instability and lack of retention of their dentures. The overdenture approach is simple, versatile, and relatively inexpensive. 3. Separate attachments, which fit to the system, should further simplify and widen the possibilities of overdenture therapy. Further research could contribute to a better selection of patients and attachments systems, especially for the maxillae. 4. Preliminary observations show a rapid loss of bone, at least for the first year, when two unsplinted abutments were used in the maxillae, retaining an overdenture by means of O-rings. We are indebted to the late Prof. M. De Clercq, former Chairman of the Department of Prosthodontics, for his helpful advice and encouragement. REFERENCES 1. Kalk W. Het kunstgebit een blij bezit? Academisch proefschrift. Amsterdam: Vrije Universiteit, 1979. 2. Ettinger RL, Taylor TD, Scandrett FR. Treatment needs for overdenture patients in a longitudinal study: five-year results. J F’EUXTHET DENT
1984;52:532-7.
3. van Steenberghe D, Quirynen M, Calberson L, Demanet M. A prospective evaluation of the fate of 697 consecutive intra-oral fixtures ad mo-
679
NAERT
4.
5.
6.
7.
8.
9. 10. 11.
12.
13.
14.
dum Br&nemark in the rehabilitation of edentullsm. J Head Neck Path01 1987;6:53-8. Engquist B, Bergendal T, Kallus T, Linden U. A retrospective multicenter evaluation of osseointegrated implants supporting overdentures. Int J Oral Maxillofac Implant 198&3:129-34. Naert I, De Clercq M, Theuniers G, Schepers E. Overdentures supported by osseointegrated fixtures for the edentulous mandible: a 2.5 year report. Int J Oral Maxillofac Implant 1988;3:191-6. Lekholm U, Adell R, Lindhe J, et al. Marginal tissue reactions at osseointegrated titanium fixtures (II). A cross-sectional retrospective study. Int J Oral Maxillofac Surg 1986;15:53-61. Quirynen M, Naert I, van Steenberghe D, Teerlinck J, Theuniers G, Dekeyser C. Periodontal aspects of osseointegrated fixtures supporting overdentures: a I-year prospective study. J Clin Periodontol (In press). Lakholm U, Zarb GA. Patient selection and preparation. In Brinemark PI, Zarb GA, Albrektason T. Osseointegration in clinical dentistry. Chicago: Quintessence Publishing Co Inc, 1985:199-209. De Clercq M. Variationsin freeway-space. Netherlands Dent 19828987. d’Hoedt B, Schramm-Scherer B. Der Periotestwert bei enossalen Implant&en. Z Zahnarstl Implantol 1988;4:89-95. Teerlinck J, Quirynen M, Darius P, van Steenberghe D. Periotest: an objective clinical diagnosis of bone apposition towards implants. Iut J Oral Maxillofac Imp1 (In press). Strid KG. Radiographic procedures. In Branemark PI, Zarb GA, Albrektsson T. Osseointegration in clinical dentistry. Chicago: Quintessence Publishing Co Inc, 1985317-27. Albrektason T, Zarb G, Worthington DP, Eriksson RA. The long-term efficacy of currently used dental implants. A review and proposed criteria of success. Int J Oral Maxillofact Implant 1986;1:11-25. Adell R, Lekholm U, Rockier B, Brinemark PI. A 15-year study of os-
15.
16.
17. 18.
19.
seointegrated implants in the treatment of edentulous jaw. Int J Oral Surg 1981;10:387-416. Adell R, Lekholm U, Rockier B, et al. Marginal tissue reactions at osseointegratad titanium fixtures. I. A 3-year longitudinal prospective study. Int J Oral Maxillofac Surg 1986;15:39-52. Cox JF, Zarb GA. The longitudinal clinical efficacy of osseointegrated dental implants A 3-year report. Int J Oral Maxillofac Imp1 1987;2:91166. Braden M, Wright P. Water absorption and water solubility of soft lining materials for acrylic dentures. J Dent Res 1983;62:764-8. Lindquist LW, Carlsson GE, Glantz PO. Rehabilitation of the edentulous mandible with a tissue-integrated fixed prosthesis: a six year longitudinal study. Quintessence Int 1987;18:89-96. Haraldson T, Jemt T, Stalblad PA, Lekhohn U. Oral function in subjects with overdentures supported by osseointegrated implants. Stand J Dent Res 1988;96:235-42.
Reprint
requests
to:
DR. I. NAERT DEPARTMENT OF PROSTHETIC CATHOLIC UNIVERSITY CAPUCIJNJZNVOER 7 B-3000 LEWEN BELGIUM
Contributing J. Teerlinck,
F. Jacob,
University
of Texas,
D.D.S.,
M.S.,*
M. D. Anderson
and Ting-Wey
Cancer
Center,
Houston,
DENTISTRY OF LEWEN
author D.D.S.,
Assistant, Department of Periodontology, Catholic University of Leuven, Leuven, Bel-
Processed record bases for the edentulous patient Rhonda
ET AL
Yen,
D.D.S.,
maxillofacial
M.S.**
Texas
Use of processed record bases to register edentulous jaw records offers increased accuracy in final prostheses occlusion. Processed bases for the maxillofacial patient following resection of the maxillae or mandible also improve the reliability of the jaw relation record. Because of the unusual paths of insertion and tissue undercuts within the surgical defect, block-out of trial record bases on the master cast can result in gross instability of the bases. Errors in occlusion, esthetics, lip support, and buccolingual tooth placement can be minimized with processed bases. (J
PROSTHETDENT~SS~;~~:~~O-~.)
A
ccurate jaw relation records are essentialfor the successfuldelivery of prostheses.Accurate record basesare required to achieve accurate records. Morrow et al.’ list four requirements of a denture record baseto achieve accuracy and stability: (1) maximum adaptation to the basal seat; (2) final border extension that is the sameas the finished denture; (3) rigidity; and (4) dimensional stability.
*Associate Dental Oncology. **Fellow in Dental 10/1/27039
660
Oncologist Oncology.
and Assistant
Professor
of Dental
Satisfying theserequirementsenhancesthe accuracy of the jaw relation record, minimizing errors in occlusion and esthetics in the final prosthesis. During fabrication of the record base,tissue undercuts must be blocked out on the master cast to allow retrieval of the base during clinical procedures.Soft material placedon the tissuesurfaceof the baseor a material, such aswax, that createsspacebetween the baseand the master cast has been advocated.lm4This block-out of the mastercast may affect oneor all of the four requirements for an accurate and stable record base. This article discussesthe use and advantages of processedrecord basesin the rehabilitation of the edentulous patient who hashad resection of the maxillae or mandible.
MAY
1001
VOLUME
66
NUMBER
6
D.D.S., Ph.D.,** and D. van Steenberghe,
fixtures
supporti,ng
M.D., Ph.D.****
Catholic University of Leuven, Leuven, Belgium Eighty-six consecutive patients, provided with 84 resilient and two nonresilient overdentures (six in the upper and 80 in the lower jaw), were examined. The overdentures were supported by a total of 173 osseointegrated titanium fixtures (the standard Branemark abutment), with a mean loading time of 19.1 months (range 4 to 48 months). In each jaw only two fixtures anchored the overdentures. No failures occurred during the observation period but two fixtures were lost before loading. The radiographic annual bone loss around fixtures in the lower jaw was -0.8 mm for the first year and less than -0.1 mm for the following years. The change in marginal bone height did not correlate with parameters such as the occlusion and articulation pattern, the presence or absence of a soft liner around the abutments, and the magnitude of the interabutment distance. The patients’ reactions to overdenture treatment were, on the whole, positive concerning chewing function, phonetics, and comfort. The need for maintenance care of the clip-bar attachment was minimal. (J PROSTAET DENT 1991;65:071-80.)
W
hile many edentulouspatients are satisfiedwith a complete denture rehabilitation to restore oral function and cosmetics,others suffer from this kind of treatment.’ The problems encountered are either functional or psychosocial,or both. Reduction of stability, retention, and load-bearing capacity have beenconsideredmajor factors for this compromised oral function. Psychosocially, patients suffer becauseof a constant fear of dentures loosening during jaw movements. Those patients who wear removable dentures do not usually seek the replacement of their unstable complete denture by a fixed prosthesis.They are pleasedwhen provided with a stable denture at limited financial expense. The functional benefitsof complete denturessupported by the retention of a few roots have been clinically documented.z It is tempting therefore to adapt the osseointegration method to the overdenture concept in patients who can accept wearing removable dentures. Preliminary results3V5 indicate the functional benefits of this technique. In addition, the overdenture concept can behelpful in some clinical situations, such as severely resorbedjaws with unfavorable jaw relations where maximal soft tissue support is required to enhancethe cosmetic and phonetic results.
*Lecturer, Department of Prosthetic Dentistry. **Professor, Department of Periodontology. ***Professor, Department of Prosthetic Dentistry. ****Professor and Head, Department of Periodontology. 10/1/262t36
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Although someof the clinical data6obtained from patients with fixed prosthesescan be extrapolated to the overdenture situation, the important clinical differences imposed the need for prolonged observation periods. This study evaluated the 4-year experience with overdenture therapy from a prosthetic point of view. The periodontal aspectsare dealt with in a companion article.7
MATERIAL From November 1984to May 1988,two or three fixtures (Branemark implants are commonly called fixtures) were installed in one or both jaws of 86 consecutivepatients. In six patients the fixtures were localized in the maxillae and in 80 patients they were localized in the mandible. Approximately three times more women (65) than men (21) were treated. The youngest patient was 33 years of age, while the oldest was77 years of age (meanage 56.5). A total of 196 Branemark implants were monitored (Nobelpharma AB, Gothenburg, Sweden). In eachmandible, two fixtures were installed in the symphysealregion, mostly in the canine region, with a connecting line parallel to the terminal mandibular hinge axis.5 A third fixture was installed in the vicinity of the midline when overdenture therapy wasbegun in our center to act asa reserve in case one of the other two fixtures would fail. Until now all but two of these third fixtures (n = 21) have remained “sleeping.” In one patient the “sleeping” fixture appeared supragingivally 1 week after the abutment connection of the other two fixtures. In this patient, the three fixtures and magnetswere usedas an attachment system. In the other
671
NAERT ET AL
I. Frequency distribution of length of loaded fixtures (N = 173) by jaw Table
No. of loaded Fixture length (mm)
Mandible
7 13 15 18 20
1. To reinforce resin base, a chrome-cobalt alloy framework was used, to which the retention clip was soldered. Fig.
0 1
0 0
Table II. Mean time of edentulousnessand number of complete dentures worn Number
O-5 y 6-15 y 16-34 y
672
0 11
before loading.
Edentulousness (n = 8.6 yr)
patient, the “sleeping” fixture wasusedbecauseof the anticipated nonintegration of the neighboring fixture (buccal dehiscenceand lingual fenestration) at the fixture installation. In the maxillae, two fixtures were installed in the canine-first premolar region. The frequency distribution and the length of the fixtures in eachjaw are presentedin Table I. The quality and resorption of the jawswere evaluated by the surgeonat fixture installation by assessing the preoperative radiographs, according to the Lekholm and Zarb classification.* Both the bone quality and quantity were noted for eachjaw. The meanquality wasmoderatefor the maxillae, Ti = 2.5 (range 1to 4) and mandible,g = 2.2 (range 1 to 4). The mean resorption anatomy wassevere for the maxillae, ii = 4.6 (range 3 to 5) and moderatefor the mandible, ‘ji = 2.4 (range 1 to 5). Most patients had an Angle classI jaw relationship (82% ), while the remaining patients were evenly distributed between classesII and III. The status of the antagonist jaw was edentulous (82% or dentate (15%); in 3% an osseointegrationfull fixed partial denture waspresent. The meantime of edentulousnesswas 8.6 years (range 0 to 34) and the average number of worn complete dentures was 2 (range 9 to 6) (Table II). Functional problemswerethe main reasonfor consultation in three quarters of the patients. These patients complained of lack of retention or stability with the existing dentureswhile eating or talking. The othershad psychosocial problems with fear of loose dentures. They would, however, accept removable dentures when retention was assured. The reason why the patients chose the overdenture therapy instead of a tissue-integrated fixed partial denture wasthe needto increasethe stability and retention of the complete denture (Table III). Another group of patients chosethe overdentures becauseof limited financial resources.Indeed, neither implants nor fixed prothesesare
Maxillae
4 47 (l)* 55 46 (l)* 6 3
10
*Lost fixture
fixtures
39%
38%
23%
0
1
of dentures (rn=2) 2
3
16% 24% 30%
15%
4
z-5
10% 5%
reimbursedby the Belgian Social Security system.In 12% of the patients, an overdenture wasmade instead of a tissue-integrated fixed partial denture becausethe patients were unable to choosefor themselves. The meanloading times for the fixtures in the mandible and maxillae were 19.7 months (range 4 to 48) and 11.7 months (range 4 to 28), respectively. The distribution of installed overdentures by year is given in Table IV. In 78 patients, in the mandible, egg-shapedDolder type bars (No. 53.01-2, Cendres et Metaux SA, Biel, Switzerland) screwedonto two fixtures were usedas an attachment system. The height of the abutment at the time of impression fabrication was 1 mm to a maximum 2 mm above the gingiva. This favored an optimal plaque control maintenance regimen and minimal leverage. A spacemaintainer 0.75 mm thick wasplacedbetweenthe bar and the retention clip before processing,and all overdentures with this retention system were reinforced by a chrome-cobalt alloy framework (Fig. 1). Approximately half of the overdentureswere processedwith a soft liner (Supersoft, Coe Laboratories Inc., Chicago,Ill.) around the bar and gold cylinders on top of the abutments. This procedurewasfollowed to lower the open spaceunderneath the overdentures, preventing food impaction and soft tissueproliferation. Supersoft liner was chosenbecauseof its goodbinding capacity to acrylic resin. Furthermore, in two patients, Rare Earth Jacksonmagnets (Solid State Inc., Mount Airy, NC.) were used. In the maxillae of one patient, a round curved bar connectedthe fixtures to a molar on both sides,thus achieving a nonresilient design.In four patients, O-rings (NobelpharmaAB) were used,and in one patient Rare Earth Jacksonmagnets were usedin the maxillae.
MAY 1991
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66
NUMBER
5
FIXTURE-SUPPORTED
OVERDENTURE
THERAPY
GAIN
Table III. Patient’s reason for choosing overdenture therapy instead of tissue-integrated prosthesis
+0.5
Reason
Frequency (TO)
Only need for increased stability
40
and retention Financial Extreme bone resorption Wanted unfixed rehabilitation Unfavorable jaw relation Advised by dentist Only advised on overdenture
mean C M 6 Ii
36 5 1 1
-1.0
1985
1986
1987
1988
1989
9
2 10
-
3
1
24
34
3
METHODS All parameterswere registeredat the time of placement of the overdentures, 1 to 2 weekslater, and from then on every 6 months up to the end of the observation period (4 to 48 months). The following prosthetic parameters were considered: (1) occlusion and articulation, (2) prosthesis stability and retention, (3) the need for relining, (4) complications of the implant components, and (5) denture materials. All complications that occurred in between the recall visits were also registered. Between November 1988and April 1989,all 866patients had a final clinical and radiographic examination by the sameperiodontist (MQ) and prosthodontist (IN). Six of the 86 patients did not return for this control visit; three had moved abroad, and the others preferred to remain with their own dentist for control assessment. Thesecolleagues
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2L-30-36
1511
All overdentures were carefully checked for balanced occlusionon the articulator and intraorally without anterior tooth contacts in the centric relation. The interocclusal spaceranged from 2 to 3 mm as measuredbetween reference points on the nose and on the chin.g The retention clips were adjusted during installation of the overdenture sothat during extreme opening of the mouth and with vigorous tongue movement the prosthesiswould not be dislodged. The interabutment distance in the mandible ranged from 8 to 29 mm (mean20 mm). In the maxillae, the interabutment distancerangedfrom 24to 39 mm (mean32 mm) measuredalongthe ridge and not alongthe connectingline. Only one fifth of the patients had not worn a transitional prosthesisbetween the fixture installation and the abutment connection.
THE
O-6 O
5 12
Table IV. Distribution (number of patients) of overdenture installation by year and by jaw
Maxillae Mandible
mm r
DENTISTRY
i
mm
LOSS.
Fig. 2. Mean change in marginal bone height for different periodsof fixture loading (number of fixtures involved).
discussedthe treatment results for these patients by telephone communication. The closebone apposition for eachfixture, after disconnecting the bars, wasevaluated clinically and radiographically. The mobility wasassessed by tapping the abutments alternatively back and forth with two instrument handles and by careful eye inspection of the bone-fixture interface on long-cone radiographs.From 1988onward, fixture mobility was also assessed by meansof the Periotest instrument (SiemonsAG, Bensheim, Germany).7*lo*r1 A fixture wasconsiderednonintegrated: first, if a free-standing fixture showedthe slightest sign of mobility; second,when a peri-implant radiolucency could be detected; and finally, if the fixture showedsignsor symptomsof pain or infection. Radiographs were made at the abutment connection with the parallel technique every 6 to 18 months.12The marginal bone height (MBH) was measured on these radiographs. The MBH was defined as the mean distance between the fixture-abutment junction and the marginal bone level mesially and distally from the fixture to the nearest0.3 mm.7This distancecorrespondsto half the distance between threads. Only those radiographswere used in which the fixture threads could easily be defined. All radiographs were examined by the sameinvestigator (MQ). Becausethe loading time ranged from 4 to 48 months and because consecutive radiographs ranged from 6 to 18 months, the data can differ for each time period. For the longitudinal evaluation, the periodical changein marginal bone height was calculated.’ The intermittent change in marginalbone height wascalculated and wasdefined asthe changein marginal bone height over a 6- to 12-month period, at two consecutiveappointments (0 to 6 months, 6 to 12 months, 12to 24 months, and 24to 36 months). Because
673
NAERT
mern c n 0 B Ii
24-30-36
24-30-36
HONTHS
24-30-36
ET AL
MONTHS
HONTHS
Fig. 3. Mean change in marginal bone height (CMBH) correlated with incisal contact (A), balanced articulation (B), interabutment distance (C), and soft liner (D) for different periods of function (number of fixtures involved).
Overdenture Frequency %
,
75
191 /
7
rl
I I &
O-b
b-12
12-18
18-Z&
2'+-30
30-36
36-42 MONTHS
Fig. 4. Frequency distribution of overdentures with soft liner (n = 42) where soft liner was still soft, by period.
of the limited number of observations in the maxillae, the change in marginal bone height could not be calculated. The gingival recession, defined as the distance from the top of the abutment to the gingival margin, was measured on six sites per abutment to the closest 0.5 mm. The hardness of the soft liner on the overdenture around
674
the abutments and bar was judged clinically. Incisal contact at centric occlusion and the articulation pattern, balanced or unbalanced, were also checked. The interocclusal space was clinically determined as the difference in distance of reference points on both the nose and chin at rest and at centric occlusion. The retentive force of each overdenture was judged by the same investigator (IN). The patient was asked to open his or her mouth as wide as possible, and to move the tongue outward. When the overdenture dislodged, a score of 0 was given. Furthermore, when the prosthesis was not loose the retention was judged by grasping the overdenture between index and thumb, above the bar, and an attempt was made to lift up the overdenture. If there was little or no resistance to move the overdenture, a score of 0 was given again. When resistance was felt, a score of 1 was given. At the final examination, the patients were asked for their reaction before and after the overdenture therapy and for their personal experience with their new overdenture. The answers for each question were given on a discontinuous analog scale with numbers ranging from 1 (very bad) to 9 (very good).
MAY
1991
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FIXTURE-SUPPORTEDOVERDENTURETHERAPY
cl
balanced
Overdenture Frequency %
balanced
became unbalanced
unbalanced
271
1
0 A
O-6
6-12
12-18
18-24
.30
24-30 MONTHS
1OC
no ~nclsal contact
0
Overdenture Frequency %
inw.1
contact
became
contact
became no contact
71 1.31
I101
\
i
O-6
6-12
12-18
18-Z&
IL
24-30
a30 MONTHS
5. Frequency distribution of overdentures with and without balanced articulation (A) and with and without incisal contact (B) and frequency of “changes” by period (number of overdentures). Fig.
RESULTS Fixture loss after
loading
During overdenture function (mean loading time: 19.7 [range 4 to 481, and 11.7 months[range 4 to 281 for the maxillae and mandible, respectively), no fixtures were either lost or showedsignsof symptomsof pain or infection. In one patient in whom a fixture had beenlost at the abutment installation, an overdenture anchored to one single fixture was designed5until a supplementary fixture was installed.
Change in marginal bone height to prosthetic parameters
in relation
The meanchangein marginal bone height for fixtures in the mandible, with egg-shapedbars asthe attachment system for different observation periods, is illustrated in Fig.
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2. For patients who had worn their overdentures for 6 months, a meanchangein marginal bone height of 0.5 mm wasobserved.For patients who had worn their overdenture for 1 year, a changein mandibular bone height of 0.75mm wasfound. During the secondyear of function, little or no changein marginal bone height could be detected (-0.01 mm). For the third year, on average,even a small“gain” of bone was observed (+0.12 mm). The change in marginal bone height wasalso analyzed in relation to the presence or absenceof incisal contact in centric occlusionand to the balancedor unbalancedarticulation at the beginningof the observation period. No correlation wasfound (Fig. 3, A and B). The interabutment distance and the use or nonuseof the soft liner in the overdenture around the retainer and abutments also played no significant role (Fig. 3, C and D).
675
NAERT
Overdenture Frequency
-
retentive
-
non-retentive
q q ’ ‘( ”
00.
0 times activated
0.0.
%
100
1211Total
Patient’s Frequency % (n-78)
0
before
m
after
ET AL
0.D O.D.
75
1201
50
25 l21Totrl
0 LL 6-12
12-24
24-48
MONTHS
Fig. 6. Periodical frequency distribution of retentive and nonretentive overdentures and number of times retention clips had been activated (number of overdentures).
0A
PCTSIV 100
Patient’s Frequency O/O
75
(n-78)
50
V. Changein interocclusal spaceby patient for different periods of overdenture wearing (number of patients) Table
Period
(mo)
O-6 6-12 12-18 18-24 24-30 30-36 36-42
+3.Smm
+2.5mm
2
+1.5mm
1
1
1
-
1
1 1
-
3 1 1
-
Soft liner properties gingival recession
-
and relation
0
15 4 5 5 6 2 3
1 1 2 1 1
to
The viscoelasticity of the soft liner material usedaround the retainer and abutments in the overdenture showeda decreasingcourse with time. In 66% of the overdentures provided with a soft liner (Fig. 4), the soft liner wasstill soft after 6 months of function;, this wasreduced to 40% after 1 year and to 8% after 2 years. The soft liner hasbeen renewed in only three patients sincethe overdenture installation. In patients wearing overdentures with soft liner around the abutments, the gingival recessionwasreduced by 60% compared with the recessionin those patients in whom no soft liner has been used.
Occlusibn,
articulation,
and vertical
height
Fig. 5 showsthe frequency distribution of overdentures with and without incisal contact, and with and without balancedocclusionfor different periodsof denture wearing. It also indicates the frequency of patients with a changed occlusal pattern at the start compared with the different evaluation periods. The group of patients that functioned with overdentures for more than 30 months showedan ar676
25
-1.5mm
0B
0I A CApN
A CApN
7. A: Frequency distribution of patients with negative subjective experiencewith their old denture and with their new overdenture. Questions asked of the patients (Yes/No response).Did you have pain or ulcerations with your old denture (P)? Did you have problemswhen chewing with your old denture (C)? Did you have problemswhen talking with your old denture (T)? Were your social contacts with others curbed becauseof your dentures (S)? Were you occupied all the time by your denture ($)? B: Frequency distribution of patients’ reactions to denture wearing before and after overdenture therapy. A, Always; C, only for chewing; Ap, only for appearance;N, never. Fig.
ticulation pattern that wasnot significantly different from that at the start. The observationsmade for the presence and absenceof incisal contact revealed a trend of losingincisal contact during the first year. For patients wearing overdentures for more than 18 months, more patients had incisal contact than those with suchcontact at the start of the study. The changein interoccusalspacefor individual patients at different periods of overdenture wearing is depicted in Table V. Sixty-eight percent of the patients had an unchangedinterocclusal spaceat these different periods.
Overdenture
retention
as a function
of time
Fig. 6 presents a histogram of the retentive and nonretentive bar-overdenture over different periods of function. All overdentures had a retention index of 1 at instal-
MAY
1991
VOLUME
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NUMBER
6
FIXTURE-SUPPORTEDOVERDENTURETHERAPY
Patlent’s
Patlent’s
%
% LO 1
40
301
30
20 -
Frequency
50
Frequency
&-A-1234567@)9
12
Patient’s
own apprcristlon
Patlent’s
own appratiatmn
3
4
5
6
1@9
Patent’s
own appreciation
Patient’s
own gprecirtmn
1234567@9
1236567@9
Patirnt’r Frequency %
56 -
1’
40-
30 -
20-
10 -
I
I
,234567@9 Patlent’s
own rpprcciatm
Fig. 8. Patients’ own appreciation of overdenture therapy on a scale of 1 to 9. 1 = Very bad; 9 = very good; 0 = median.
lation and after 1 or 2 weeks of function. The need for reactivation of retention clips or bars did not change appreciably in time. The clips were reactivated after 6 to 12 months of function in 3 of 23 patients, after 12 to 24 months in 4 of 21 patients, and after 24 to 48 months in 12 of 27 patients.
dian for these answers lies in score 8. Eighty percent of the patients answered positively regarding the question concerning the presence of food particles under the overdenture after meals. Sixty-five percent of them found this annoying.
Patients’
The complications during overdenture wearing are summarized in Table VI. The complications for the maxillary overdentures were related to the attachment systems. Bad experiences with the Jackson magnets required stopping their use. Corrosion and rapid loss of retention and extreme wear were the main reasons for this decision. O-ring box fracture occurred twice on eight O-rings, although they had been in place for only 5 months. The complications for the maxillary overdenture at the implant components are not reliable because of the limited number of treated patients. More important are the complications for the mandibular overdentures. Loose gold screws, the main complication at the implant component level, occurred in 5 % of the patients. Opposing complete denture fracture occurred in
reactions
Fig. 7 graphically depicts changes in negative subjective experiences and changes in denture wearing before and after overdenture installation. After overdenture installation, six patients still complained of pain when chewing. This pain was caused by pressure of the overdenture on the mental nerve or spiny residual ridges in very resorbed jaws. Psychologic problems persisted in two patients who asked for fixed prostheses where anatomic limitations precluded the installation of more than two fixtures. All patients except one always wore their overdentures. This same compliance pattern had only been 80% before overdenture therapy. The patients’ own appreciation on the whole scored very positive on the rating scales (Fig. 8). The me-
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Complications
677
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Table
VI.
Number of overdenture complications Maxillae
components (U:12/L:161) Abutment screwloose Goldscrewloose
Mandible
Implant
0
2
2 8 (5)
0
1
2
5 (100)
Overdenture parts
Reinforcingframeworkfracture (u:2/L:78) Corrosionand lossof retention of the Jacksonmagnets (l&2&5)
0 ring box fracture (US/L:O)
2
-
Opposing complete denture fracture -
(L:O/u:71) U, Upper jaw; L, lower jaw. Numbers in parentheses are percent
7 (10)
of cases.
10% of the patients. Even one overdenture chrome-cobalt alloy reinforcement fractured. Only six overdentures required relining. Treatment for gingival proliferation occurred in eight patients.
DISCUSSION The failure rate of loaded fixtures in this seriesof nongrafted and nonirradiated jawbonesrehabilitated by means of resilient overdentures is 0% over a 4- to 48-month period. Our failure rate after loading for the mandibular overdenture is in accordance with the less than 1% reported by other centers.4These data for the failure rate are only significant for the mandible. Becauseof the limited number involved in the present study, no conclusions can be drawn for the maxillae. Another restriction is the observation time, with an averageof 19.7months of function; this is far below the minimum of the 5 years requested.lOHowever, it isknown that if failures occur with Branemark implants, thesetake placeduring the healingor remodeling phase.l3 One could prudently extrapolate the present data to a long-term perspective, although this was only proved for implant-supported prostheses.14 The range and timing of bone level changesobservedapproachngthe zero line after 1 year are similar to those for fixtures supporting fixed prostheses,6p I53l6 which suggestsa favorable long-term prognosisfor overdentures in the mandible. The gain in meanbonelevel asobservedafter the second year is in agreementwith the results reported by Cox and Zarb.16A possibleexplanation is that in time bone remodeling occurs, resulting in the apposition of cortical bone, which becomesmore visible on radiographs.The difference observedover time wastoo consistentduring this period to be due to a measurementerror. The better results obtained for overdentures in the mandible when comparedwith complete fixed prostheses can be explained by the opportunity of selectinga site with optimal bonequality when only two fixtures have to be installed. The patient group in this study, contrary to that of 678
ET AL
the Swedishmulticenter study,4 did not consistof patients for whom it is anatomically impossibleto install more than two fixtures. On the contrary, in nearly all but five patients a fixed prosthesison four to six implants was a possible treatment alternative. Another reasonfor the excellent results wasthe overdenture designitself. By using only two fixtures with an interconnection parallel to the hinge axis, a resilient overdenture designis possible;this guarantees free rotation during dorsal loading, resulting in a twist-free load transmissionto the fixtures in a nearly axial direction. The absenceof anterior incisal contact in centric occlusionand the existenceof balancedarticulation in complete denture treatment have been advocated to favor the load distribution on the underlying supporting structures. The greater the interabutment distance, the greater are the loading forces on the fixtures. Absenceof anterior contact, presenceof balanced articulation, the use of a soft liner, and small interabutment distance contributed to the positive fixture-bone interface. However, the relationship between the change in marginal bone height and these mentioned factors could not be sustained. It should be mentionedthat the data werecross-sectionalin nature and thus the interindividual differences could have masked possiblelessimportant relationships.However, becauseof the high number of subjectsper observation, this risk was minimized. Therefore it is concludedthat the four abovementioned factors do not correlate with the change in marginal bone height for this period of observation. Proliferation of the gingiva around overdenture abutments, whether natural teeth or titanium implants, is a well-known fact.2p4 In the Swedishmulticenter study,4 hyperplasiatreatment occurred in 25% of the patient group. However, in this study only a few patients were observed, and this happened in the earlier treatment period. In patients in whom movable oral mucosasurroundedthe abutments, a gingival graft was performed around three abutments. This graft was only partially successfulin coping with the gingival overgrowth. An attempt to fill the dead spacearound the abutments with a soft liner did not fulfill the objectives either. Indeed, less gingival recessionwas observedwhen a soft liner was applied. Stringent oral hygiene and a nontraumatic overdenture designfor the soft tissueswill maintain healthy soft tissues.The premature insertion of the overdenture after the abutment connection also seemsto favor hyperplasia of the gingiva. A wait of some weeksto allow sufficient soft tissuehealing is recommended. After 1 year, soft liners harden in two thirds of the patients. The soft liner should be renewedat least every year if viscoelasticproperties are to be maintained.17It may be questionableto usea soft liner in the overdenture for the previously stated goal. IncisaI contact and articulation pattern may not be stable over time. However, checking incisal contact in centric occlusion showed changesover time. It should be rememberedthat 82% of the patients had a completedenture in the oppositejaw, which doesnot
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favor stability in recording. The incisal and articulation pattern were always registered at the overdenture installation and not after 1 or 2 weeks of function, the period of time needed for complete denture settling. In contrast to occlusion and articulation, the mean interocclusal space remained constant over the entire follow-up period. This fact does not contradict the previous assumption concerning difficulties of monitoring the denture position with precision after many months. Indeed, the interocclusal space relates to physiologic parameters such as muscle tonus and can adapt in time.g After the bar-attached overdentures had been functioning for 2 to 4 years, 72% of the overdentures were properly retained. Of the 71 bar-attached overdentures observed, five were in need of maintenance more than twice. The bar concept involves more effort from the dentist and the technician than the use of magnets, O-rings, or other nonsplinted abutment attachment systems. The long-term maintenance of the bar concept is only restricted by the activation of the retention clip. The manufacturers of the clip attachments should be stimulated to provide a device by which one could objectively quantify the retentive force of the clips, thereby preventing overactivation of the clip, which could lead to long-term harmful effects of the implant components or even to the fixture-bone interface. The patients’ own appreciation of the overdenture was, as in other studies,4 positive. Ninety-seven percent found the overdenture better than the previous denture, and about 95% never or only once daily removed their overdenture due to discomfort. Before treatment, 60% of the patients used denture adhesives, while none did so after overdenture treatment. Although the patients were satisfied with their overdentures, about one fourth of them would choose a fixed prosthesis over an overdenture if the treatment had to be repeated and/or when costs were not a hindrance. Patient selection should be considered carefully when an overdenture with a resilient design is advised instead of a fixed partial denture. Overdentures should be contraindicated (1) when patients with a favorable anatomy and jaw relations ask for a fixed prosthesis; (2) in patients who show advanced resorption in the mandible, with sharp, spiny ridges, and where the foramina mentales are superficially localized; (3) in patients who cannot accept the conditions that food impaction occurs under the overdenture and that the overdenture should be cleaned after meals-it may not be possible to lift up the overdenture with the tongue to sweep away food particles; and (4) when none of these criteria are met but when the patients cannot accept wearing removable dentures for psychologic reasons. The overall material drawbacks of bar-attached overdentures in the mandible were, apart from the use of a soft liner and its hardening, limited to one fracture of the Cr-Co reinforcement. This fracture presumes that bite force levels with overdentures are considerable. An increased number of midline fractures of conventional max-
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DENTISTRY
illary dentures after osseointegrated prosthetic treatment was also reported.ls Only six patients needed a relining of the overdenture base. Tilting and shifting forces, which are known to be the most detrimental for bone resorption, are rarely present in the bar-attached overdenture concept. A delayed bone resorption can be expected when compared with bone resorption under a complete denture. Moreover, more patients complained about less retentive maxillary complete dentures. Improved comfort with mandibular overdentures1g might be an explanation of the fact that patients unconsciously tend to compare the maxillary denture with the well-retained mandibular denture. Whereas no adverse tissue reactions were found when magnets were applied, it seems that with the use of O-rings, rapid bone loss around the fixtures occurs, at least in the maxillae.7 Because of the limited number of patients treated with magnets and O-rings, no conclusions can be made. Follow-up studies where fixtures are interconnected and not interconnected, and where different attachment systems are in use are presently in progress.
CONCLUSIONS From the observations made in this study, the following preliminary conclusions can be formulated. 1. Osseointegrated oral implants can be used with low failure rates, at least over a medium-term period, for resilient overdenture therapy in the mandible. Not a single failure occurred for bar-attached overdentures retained by a bar on two fixtures in the mandible when grafted and irradiated jaws were excluded. 2. The overdenture approach seems to be useful in patients who accept removable dentures, but who are handicapped because of instability and lack of retention of their dentures. The overdenture approach is simple, versatile, and relatively inexpensive. 3. Separate attachments, which fit to the system, should further simplify and widen the possibilities of overdenture therapy. Further research could contribute to a better selection of patients and attachments systems, especially for the maxillae. 4. Preliminary observations show a rapid loss of bone, at least for the first year, when two unsplinted abutments were used in the maxillae, retaining an overdenture by means of O-rings. We are indebted to the late Prof. M. De Clercq, former Chairman of the Department of Prosthodontics, for his helpful advice and encouragement. REFERENCES 1. Kalk W. Het kunstgebit een blij bezit? Academisch proefschrift. Amsterdam: Vrije Universiteit, 1979. 2. Ettinger RL, Taylor TD, Scandrett FR. Treatment needs for overdenture patients in a longitudinal study: five-year results. J F’EUXTHET DENT
1984;52:532-7.
3. van Steenberghe D, Quirynen M, Calberson L, Demanet M. A prospective evaluation of the fate of 697 consecutive intra-oral fixtures ad mo-
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5.
6.
7.
8.
9. 10. 11.
12.
13.
14.
dum Br&nemark in the rehabilitation of edentullsm. J Head Neck Path01 1987;6:53-8. Engquist B, Bergendal T, Kallus T, Linden U. A retrospective multicenter evaluation of osseointegrated implants supporting overdentures. Int J Oral Maxillofac Implant 198&3:129-34. Naert I, De Clercq M, Theuniers G, Schepers E. Overdentures supported by osseointegrated fixtures for the edentulous mandible: a 2.5 year report. Int J Oral Maxillofac Implant 1988;3:191-6. Lekholm U, Adell R, Lindhe J, et al. Marginal tissue reactions at osseointegrated titanium fixtures (II). A cross-sectional retrospective study. Int J Oral Maxillofac Surg 1986;15:53-61. Quirynen M, Naert I, van Steenberghe D, Teerlinck J, Theuniers G, Dekeyser C. Periodontal aspects of osseointegrated fixtures supporting overdentures: a I-year prospective study. J Clin Periodontol (In press). Lakholm U, Zarb GA. Patient selection and preparation. In Brinemark PI, Zarb GA, Albrektason T. Osseointegration in clinical dentistry. Chicago: Quintessence Publishing Co Inc, 1985:199-209. De Clercq M. Variationsin freeway-space. Netherlands Dent 19828987. d’Hoedt B, Schramm-Scherer B. Der Periotestwert bei enossalen Implant&en. Z Zahnarstl Implantol 1988;4:89-95. Teerlinck J, Quirynen M, Darius P, van Steenberghe D. Periotest: an objective clinical diagnosis of bone apposition towards implants. Iut J Oral Maxillofac Imp1 (In press). Strid KG. Radiographic procedures. In Branemark PI, Zarb GA, Albrektsson T. Osseointegration in clinical dentistry. Chicago: Quintessence Publishing Co Inc, 1985317-27. Albrektason T, Zarb G, Worthington DP, Eriksson RA. The long-term efficacy of currently used dental implants. A review and proposed criteria of success. Int J Oral Maxillofact Implant 1986;1:11-25. Adell R, Lekholm U, Rockier B, Brinemark PI. A 15-year study of os-
15.
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seointegrated implants in the treatment of edentulous jaw. Int J Oral Surg 1981;10:387-416. Adell R, Lekholm U, Rockier B, et al. Marginal tissue reactions at osseointegratad titanium fixtures. I. A 3-year longitudinal prospective study. Int J Oral Maxillofac Surg 1986;15:39-52. Cox JF, Zarb GA. The longitudinal clinical efficacy of osseointegrated dental implants A 3-year report. Int J Oral Maxillofac Imp1 1987;2:91166. Braden M, Wright P. Water absorption and water solubility of soft lining materials for acrylic dentures. J Dent Res 1983;62:764-8. Lindquist LW, Carlsson GE, Glantz PO. Rehabilitation of the edentulous mandible with a tissue-integrated fixed prosthesis: a six year longitudinal study. Quintessence Int 1987;18:89-96. Haraldson T, Jemt T, Stalblad PA, Lekhohn U. Oral function in subjects with overdentures supported by osseointegrated implants. Stand J Dent Res 1988;96:235-42.
Reprint
requests
to:
DR. I. NAERT DEPARTMENT OF PROSTHETIC CATHOLIC UNIVERSITY CAPUCIJNJZNVOER 7 B-3000 LEWEN BELGIUM
Contributing J. Teerlinck,
F. Jacob,
University
of Texas,
D.D.S.,
M.S.,*
M. D. Anderson
and Ting-Wey
Cancer
Center,
Houston,
DENTISTRY OF LEWEN
author D.D.S.,
Assistant, Department of Periodontology, Catholic University of Leuven, Leuven, Bel-
Processed record bases for the edentulous patient Rhonda
ET AL
Yen,
D.D.S.,
maxillofacial
M.S.**
Texas
Use of processed record bases to register edentulous jaw records offers increased accuracy in final prostheses occlusion. Processed bases for the maxillofacial patient following resection of the maxillae or mandible also improve the reliability of the jaw relation record. Because of the unusual paths of insertion and tissue undercuts within the surgical defect, block-out of trial record bases on the master cast can result in gross instability of the bases. Errors in occlusion, esthetics, lip support, and buccolingual tooth placement can be minimized with processed bases. (J
PROSTHETDENT~SS~;~~:~~O-~.)
A
ccurate jaw relation records are essentialfor the successfuldelivery of prostheses.Accurate record basesare required to achieve accurate records. Morrow et al.’ list four requirements of a denture record baseto achieve accuracy and stability: (1) maximum adaptation to the basal seat; (2) final border extension that is the sameas the finished denture; (3) rigidity; and (4) dimensional stability.
*Associate Dental Oncology. **Fellow in Dental 10/1/27039
660
Oncologist Oncology.
and Assistant
Professor
of Dental
Satisfying theserequirementsenhancesthe accuracy of the jaw relation record, minimizing errors in occlusion and esthetics in the final prosthesis. During fabrication of the record base,tissue undercuts must be blocked out on the master cast to allow retrieval of the base during clinical procedures.Soft material placedon the tissuesurfaceof the baseor a material, such aswax, that createsspacebetween the baseand the master cast has been advocated.lm4This block-out of the mastercast may affect oneor all of the four requirements for an accurate and stable record base. This article discussesthe use and advantages of processedrecord basesin the rehabilitation of the edentulous patient who hashad resection of the maxillae or mandible.
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