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The Evidence for Immediate Loading of ImplantsDavid L. Cochran,
DDS, PhDFrom the Departments of Periodontics, The University of
Texas Health Science CenterSan Antonio, San Antonio, TX
INTRODUCTION
Many clinicians today recommend implant therapy for pa-tients
requiring tooth replacement. This therapy can providea highly
successful restoration of both function and esthetics.As such, more
and more dentists are providing restorationsand patients are
demanding these restorations. Along withsuch an increase in
procedures comes a desire to simplify theexperience in regard to
many aspects including the time in-volved from starting the
restoration to finishing the proce-dure. The shortest amount of
time involved would be toplace the restoration on the implant
immediately after thesurgical placement of the implant, a procedure
called imme-diate restoration and/or loading. While immediate
loadinghas been discussed in the literature and papers report on
thistechnique, this procedure has not gained widespread
accep-tance. To understand the possibilities of immediate
loading,one must take a careful look at the implant procedure from
ahistorical perspective, from a biological perspective, and froma
prospective of the available literature on the topic. This isthe
focus of this report.One confounding area when discussing immediate
loading
or any loading protocols is how various terms are
defined.Different investigators define certain terms different
waysand this can change the interpretation of the results of
studies.An example is how Bimmediate loading[ is defined or even
theterm Bloaded.[ Some investigators suggest that placing animplant
into bone and submerging it below the soft tissuesresults in
loading of the implant. The rationale is that flextureof the
jawbone upon opening and closing and during chewingexerts forces on
the implant and thus Bloading[ the implant.Others would suggest
that an implant is loaded when it be-comes visible in the oral
cavity. This would occur when a non-submerged implant is used or
when a submerged implantsclosure screw becomes exposed through the
soft tissue. Therationale here is that tongue movements, cheek
pressure, andfood could impact the top of the implant therefore
placing aBload[ onto the implant. Other individuals would suggest
thatthe implant is not Bloaded[ until a temporary restoration
orimplant component of some shape is placed onto the implant
and is in the oral cavity but is not in occlusion with the
op-posing dentition. Again the rationale in these cases would
betongue and cheek movements and food that would contact
thetemporary restoration and the opposing dentition. Last,
otherinvestigators and authors define Bloading[ as when the
im-plant restoration is in direct contact with the opposing
denti-tion. This is usually confirmed in centric occlusionwith
coloredocclusal marking paper or shim stock. This is a more
objectivemeasure of loading and the term that will be used in this
reportfor the loading of an implant restoration.
HISTORICAL PERSPECTIVE
To understand the loading of implants, it is necessary to
ap-preciate how loading protocols were established.
Loadingprotocols were arrived at originally by Branemark and
asso-ciates1 while working out clinical protocols for placing
im-plants. These investigators described 3 distinct phases
ofdevelopment in the technique, which resulted in improvedsuccess
rates after each stage of trial and error. The initial stageof
development lasted from the mid 1960s until 1968. A de-velopment
phase followed from 1968 until 1971 and then aroutine stage for the
technique followed from 1971 until 1975.During the early and
development stages, one aspect that wasinvestigated was loading
protocols. Various healing times wereevaluated and it was
determined that shorter healing times re-sulted in failure of the
implants. These findings suggested thata healing time of 3 months
was required in the mandible and6 months of healing was required
for the maxilla. These heal-ing times were used by clinicians and
in many studies and, assuch, 3 months in the mandible and 6 months
in the maxillabecame recognized as conventional healing times.The
clinical experience that suggested a 3- and 6-month
healing time in the mandible and maxilla respectively did
notsuggest a biological rationale for such a
recommendation.Szmukler-Moncler et al2 speculate on 4 possible
biologicalevents that could account for the required healing times
clini-cally established by Branemark et al.1 The first
possibilitywas that early loading would result in fibrous
encapsulationof the implant and no osseointegration. A second
possibilitywas that the overheated bone tissue, which undergoes
necro-sis from the osteotomy preparation, needs to be replaced
andduring this time the tissue is not capable of supporting
theimplant. A third possibility suggested was that the necroticbone
created during osteotomy preparation is rapidly re-modeled and
turned over and that during the remodeling,the strength of the bone
to implant contact is compromised.Last, it was speculated that the
3- to 6-month healing period
Presented at the 2nd Evidence-Based Dentistry ConferenceNovember
6, 2005Chicago, Illinois
J Evid Base Dent Pract 2006;6:155
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was required in order to remodel bone adjacent to the
bone-implant interface. This adjacent bone remodeling could
com-promise the ability to support the implant. Thus,
severalscenarios were envisioned that could explain why an
extendedhealing period was required prior to loading of the
implant.The findings regarding healing times established by
Branemark et al1 were reinforced by work performed byRoberts.3
These latter findings suggested that the same heal-ing periods were
required prior to loading the implant. With-out such a healing time
prior to loading, the bone to implantinterface was thought to be
damaged by loading. Such reportsled to the establishment of the
conventional healing periods.These healing times were also
reinforced by work during the1970s in the orthopedic field.4
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process was critical. In the final third phase, the
RefinementPeriod, shortened healing protocols have been
investigatedand immediate loading protocols have been examined
underdefined conditions. This Refinement Period has been oc-curring
in the last 5 to 6 years since 2000. These evolutionaryperiods have
translated to patient care such that in the De-velopment Period,
techniques were developed to replaceteeth in edentulous patients.
During the Exploratory Period,these techniques were extended to
provide tooth replacementin partially edentulous patients, and in
the Refinement Periodall these techniques are being optimized (Fig.
2).Features of the evolutionary periods in implantology in-
clude the following. In the Development Period, the tech-niques
were begun in edentulous patients, the techniqueswere developed so
that they became predictable, biocompat-ible materials were used,
many implants were placed in eachpatient, the implants had long
undisturbed healing times of3 to 9 months, implants were placed in
high-quality (pre-dominantly cortical dense) bone, cross-arch
stabilization wasused, the opposing dentition was a denture, and,
most signi-ficantly, there was minimal heating of the bone tissue
duringimplant surgery. The outcome of the Development Periodwas
help for the denture patient.During the Exploration Period, the
implant technique be-
gan to be applied to partially edentulous patients. The
sameprinciples that had been learned in edentulous patients
wereassumed to be valid for partially edentulous patients;
how-ever, various aspects of the techniques were examined fortheir
necessity since different clinical indications were beingused. Some
questions that were raised and that have beenexplored include the
following: could the material the im-plants were made from change
(eg, alloys of titanium ratherthan pure titanium), could you oppose
teeth or fixed partialdentures rather than dentures with the
implant restoration,was cross-arch stabilization required, could
the implants beplaced in lower quality bone, was bicortical
stabilization nec-essary, could fewer implants be used including
just a singleimplant, did you need to cover (submerge) the implant
underthe soft tissues in order to achieve osseointegration
(although
Andre Schroeder had been using nonsubmerged implantssince the
1970s12), could you load the implant prior to the3- to 9-month
healing time, and could you place the implantinto extraction sites?
The answers to these questions helped todefine the implant
technique in partially edentulous patientsand thus benefited those
patients missing 1 or more teeth.By the time of the Refinement
Period, dental implant place-
ment became a routine successful tooth replacement therapyfor
both edentulous and partially edentulous patients. Re-search during
this time focused on optimizing surface char-acteristics of the
implant including both morphology andchemistry and exploring ways
to further shorten the healingtimes of the implant prior to
restoration and loading, with theultimate goal of loading the
implant immediately, meaning atthe time of implant placement. Also
during the RefinementPeriod, tissue-engineering techniques were
introduced to en-hance the rate of healing and the quantity and
quality of bonetissue around the implant (eg, the bone-to-implant
contact).The outcome of these improvements during the
RefinementPeriod led to the use of implant therapy to replace
missingteeth in more indications and thus more patients.
BIOLOGICAL CONSIDERATIONS
Loading protocols for endosseous dental implants can bestbe
interpreted on the biologic basis of how the tissues re-spond to
implant placement. In fact, few appear to realize
thatosseointegration occurs instantaneously on implant place-ment.
Osseointegration was first defined as bone-to-implantcontact at the
light microscopic level and then later defined asa direct
structural and functional connection between or-dered living bone
and the surface of a load-carrying im-plant.1 Cochran et al,13 in a
study of the bone response toimplants with 2 different surface
characteristics, stated thatwhen an implant is placed clinically
into an osteotomy pre-paration, that the bone directly contacts the
implant surface.This results in immediate osseointegration of the
implant asdefined by direct bone-to-implant contact if analyzed at
thelight microscopic level. In fact, when an osteotomy site
isprepared, bone tissue is cut to a dimension of the implantdrill.
This leaves edges of the bone surrounding the hole leftby the
drill. More dense bone is found in the cortical areaswhile less
dense bone, in the form of interrupted trabeculae,are found in
areas of cancellous bone. When an implant isthen placed into the
preparation, especially if the implant hasa slightly larger
diameter than the implant drill, the implant isBpress-fit[ along
the cut bone edges and the implant contactsthe bone, ie, is
osseointegrated (bone-to-implant contact at thelight microscopic
level). These areas of bone contact with theimplant surface are
referred to as Bprimary bone contact.[13
Histologic analysis of such bone reveals intimate contact ofthe
bone with the implant surface (osseointegration) includ-ing
lamellar plastic deformation, elongated Haversion sys-tems, and
micro-fractures in the bone (Fig. 3). Because bonetissue is dynamic
and remodels over time, these areas of bonecontact are remodeled
and are replaced by new bone. This
Figure 2. Decades listed for the 3 development periodsalso
listing the predominant patients treated.
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Volume 6, Number 2 157Cochran
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new bone contact is termed Bsecondary bone formation.[At the
same time, new bone is also formed on the implantsurface
(especially if the surface is osteoconductive) in areasbetween the
areas of primary bone contact. This new boneis also termed
Bsecondary bone formation.[ Thus, at earlytime points there is a
lot of primary bone contact alongthe implant surface (dependent on
the existing quantityand quality of bone at the implant site) and
very little sec-ondary bone formation. At later time points,
however, theratio reverses such that primary bone contact decreases
andsecondary bone contact increases. This can be viewed
dia-grammatically as is shown in Fig. 4.Histological analyses of
large numbers of implants in pa-
tients is not possible, so clinical alternatives have been
usedto determine if an implant is osseointegrated. One such
sur-
rogate for osseointegration is to determine if the implant
isstable in the jaw. Several methods are available to
evaluatestability and one more recent way is to use resonance
fre-quency analyses. Barewal et al14 have followed the stability
ofimplants over early healing times with resonance
frequencymeasurements. Their findings indicated that implants
placedin areas of high bone quality are relatively stable over
theearly healing periods. However, as the quality of bone
de-creases, the stability of the implant decreases over the first3
to 4 weeks with the least stability found for those implantsin the
lowest bone quality (Fig. 5). These findings suggestthat implants
placed in high-quality bone are surrounded byenough primary bone
contact that stability of the implantis maintained by the primary
contact while the remodelingand formation of new bone can occur to
such a degree as tofurther maintain the stability as measured by
resonance fre-quency analyses (Fig. 6 and Fig. 7). However, when
the im-plant is placed into a site with poor bone quality, very
littleprimary contact exists around the implant (Fig. 8 and Fig.
9).As remodeling occurs, the implant becomes less stable be-cause
(1) the remodeling process in this case takes place in arelatively
high percentage of the bone surrounding the im-plant (little
bone-to-implant contact initially because of poorbone quality;
therefore, as remodeling occurs, this representsa large proportion
of that small amount of bone), and (2)there has not been sufficient
time for new bone to form (sec-ondary bone formation). Thus,
stability of the implant asmeasured by resonance frequency analyses
reveals a sig-nificant decrease in stability between the time of
primarybone contact remodeling and the formation of new boneor
secondary bone contact. Therefore, the clinical stabilityof
implants in bone, as measured by resonance frequencyanalyses,
reflects the biological processes that are ongoing atthe
bone-to-implant interface. These events further empha-size that
Bosseointegration[ is not a static event but ratherrepresents a
Bdynamic equilibrium[ at the site of bone-to-implant contact. Thus,
given this understanding, a new
Figure 3. Primary contact of implant with cortical bone.Original
magnification: X25. Compression of the corti-cal bone can be
observed. Reprinted with permissionfrom Cochran DL, Schenk RK,
Lussi A, HigginbottomFL, Buser D. Bone response to unloaded and
loaded tita-nium implants with a sandblasted and acid-etched
sur-face: a histometric study in the canine mandible. J BiomedMater
Res. 1998 Apr;40(1):1-11.13
Figure 4. Schematic of bone contact against an implantsurface
and what happens to the bone over time.
JOURNAL OF EVIDENCE-BASED DENTAL PRACTICE
158 Cochran June 2006
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definition of osseointegration could be Bstability of animplant
in bone that represents a dynamic equilibrium be-tween existing
native bone (primary bone contact) and re-modeling and new bone
formation (secondary bone contact),and its maintenance, at the
bone-implant interface[ (Fig. 10).
LITERATURE EXAMPLES
Understanding the biological consequences of implant
inte-gration allows an appreciation of what is possible in regardto
the loading of implants. These events are then reflectedby the
literature on loading protocols. For instance, under-standing that
implants placed in excellent bone quality will
be stable over the early healing periods and remain
stable(osseointegrated as defined above), suggests that
multipleimplants placed in the anterior mandible and are rigidly
fixedorally can be successfully loaded. Thus, publications
byBabbush et al,15 Schnitman et al,16 Tarnow et al,17 andChiapasco
et al18 are not surprising. Loading protocols inother indications
are certainly possible but the implant sitesmust be carefully
chosen as to reflect sites that can have highbone quality, the
implant restoration can be stabilized byadjacent tooth structure
etc, where implant stability can bemaintained in the transition
from primary bone contact tosecondary bone contact. This is
reflected in papers publishedand in reviews of literature on this
topic as noted below.
Figure 5. Stability of implants in different qualities of bone
as detected by resonance frequency analyses over time. ISQis the
implant stability quotient. Reprinted with permission from Barewal
RM, Oates TW, Meredith N, Cochran DL.Resonance frequency
measurement of implant stability in vivo on implants with a
sandblasted and acid-etched surface. IntJ Oral Maxillofac Implants.
2003 Sep-Oct; 18(5):641-51.14
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An example of a recent study evaluating implant loadingprotocols
examined various healing periods prior to loadingincluding no
healing period, 10 days, 21 days, and 3 monthsof loading.19 Teeth
were extracted bilaterally in the caninemandible and after 5
months, implants were placed at dif-ferent time points such that
each animal received 3 implantsat each of the 4 healing times. All
gold, screw-retained crownswere placed on all the implants the same
day and radio-graphs taken at monthly intervals until the study
animalswere killed at 3 months post-loading. Block sections were
ob-tained from each implant site and histological analyses
wereperformed in addition to the monthly radiographic analyses(Fig.
11 and Fig. 12). No implants were lost in spite of thevarying
loading times and occlusal wear on the gold crowns.
The conclusions demonstrated that no significant differenceswere
found between the implants loaded after different heal-ing times as
evaluated clinically, radiographically, and his-tologically. Thus,
both immediate and early loading of theimplants did not have
adverse effects on the survival or suc-cess of the implants.A
meta-analysis was performed on more than 1000 im-
plants in patients and compared loading times as evaluatedby
implant survival.20 This article analyzed 13 prospectiveclinical
trials, 6 of which were randomized. Overall, nosignificant
differences were detected between loading proto-cols. Furthermore,
although a higher actual number of fail-ures occurred in the early
loading protocols (2 to 6 weeks ofhealing prior to loading)
relative to the conventional loading
Figure 6. The change in primary bone contact when animplant
placed in a site with a large proportion of densebone such as
cortical bone.
Figure 7. The stability of an implant placed in high qual-ity
bone is large (represented by a small gray area).
Figure 8. The change in primary bone contact when animplant is
placed in a site with a large proportion of lessdense bone such as
cancellous bone.
Figure 9. The lack of stability of an implant placed inlow
quality bone (represented by large gray area).
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160 Cochran June 2006
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protocol, there was no significant difference in the
implantfailure rate between loading protocols. It should be
notedthat conventional loading was defined as 3 to 6 months
andimmediate loading from 1 to 2 days; however, early
loadingincluded studies with a range of healing times (less than14
days, within the first 35 days, and within the first 6weeks). The
authors noted a number of limitations of theirstudy including only
6 randomized studies out of a total13 studies, only 1266 implants
evaluated, all the trials beingunderpowered, and the clinical
heterogeneity of the studies.
An implant consensus conference was held in Gstaad,Switzerland,
in 2003 by the International Team for OralImplantology. One group
at the consensus meeting eval-uated immediate and early loading
restoration and loadingprotocols for dental implants.21 Three
papers were submittedthat evaluated loading protocols in the
literature related toedentulous patients,22 partially edentulous
patients,23 andclinical techniques.24 After careful analyses and
evaluation ofthe literature reviews, an international group of 17
cliniciansmade recommendations on loading protocols based on
theliterature and the collective experience of the group. Thisgroup
determined that the volume of literature on loadingprotocols was
moderate and the evidence was limited at bestfor the procedures
considered. The predominant literaturewas case reports. Loading was
defined as contact with theopposing dentition as opposed to
restoration without contact.Conventional healing was defined as 3
months postYimplantplacement until restoration, whereas immediate
restorationwas defined as restoration within 48 hours of implant
place-ment but not in occlusion with the opposing dentition.
Thisdefinition was based on the capacity to perform the
restor-ative clinical procedures within a limited time frame
fromsurgery (such as the surgical placement occurring in oneoffice
one day and the restorative procedures performed in
Figure 10. New definition of osseointegration reflectingthe
dynamic biological processes that occur around an im-plant placed
in bone.
Figure 11. Histologic cross-sections of implants from a) Group
A: 3 months, b) Group B: 21 days, c) Group C: 10 days,d) Group D: 2
days after 3 months of loading. Reprinted with permission from
Quinlan P, Nummikoski P, SchenkR, Cagna D, Mellonig J, Higginbottom
F, Lang K, Buser D, Cochran D. Immediate and early loading of SLA
ITIsingle-tooth implants: an in vivo study. Int J Oral Maxillofac
Implants. 2005 May-June;20(3):360-70.19
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Volume 6, Number 2 161Cochran
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another office the next day). Early restoration was defined
asthe placement of the restoration at least 48 hours subsequentto
implant placement but not later than 3 months. Immediateloading was
therefore defined as restoration within 48 hoursof implant
placement and occlusal contact with the opposingdentition. Early
loading was therefore restoration at least48 hours subsequent to
implant placement but not later than3 months and the restoration in
contact with the opposingdentition. The consensus group noted that
the results ofthe studies were obtained from conditions that were
con-sidered favorable in that the inclusion and exclusion
criteriaused in many of the studies limited their evaluation to a
se-lected population.The consensus conference concluded that in the
edentu-
lous mandible, immediate loading (up to 48 hours) in
patientswith both overdentures and fixed prostheses was well
doc-umented in the literature (Fig. 13). Early loading was
sepa-rated into 2 periods based on studies in the literature.
Oneearly loading period was between 48 hours and 6 weeksand the
second period from 6 weeks to 3 months. In theedentulous mandible
in the period of early loading from48 hours to 6 weeks, the
procedure for overdentures andfixed prostheses was not well
documented. In the period from6 weeks to 3 months, no overdenture
literature was availablebut the literature on fixed prostheses was
well documented.In regard to the edentulous maxilla, no literature
was avail-
able on overdentures that involved immediate or early load-ing
(Fig. 14). In regard to fixed prosthesis in the edentulousmaxilla,
literature was available on both immediate and earlyloading;
however, the group determined that this procedurewas not well
documented in the literature. In regard to thepartially dentate
maxilla andmandible, overdentures were not
applicable (Fig. 15). Fixed prostheses used in immediate
res-toration or loading indications in the partially dentate
patientwere not well documented. In regard to early restoration
orloading in the partially dentate patient, the procedure waswell
documented only after 6 to 8 weeks and then when animplant was used
with a roughened titanium surface.
CONCLUSION
A summary of loading protocols, based on historical
de-velopment, biological considerations, and the literature
in-dicate that shortened loading protocols are dependent on (1)the
quantity and quality of bone at the implant site and, asa
consequence, the amount of primary bone contact, and(2) the
rapidity of the bone formation and remodeling of the
Figure 12. Tissue-to-implant contact between tissueand primary
and secondary bone, bone marrow, and con-nective tissue for Groups
A (3 months), B (21 days), C(10 days), and D (2 days). Bars
indicate SE. Reprintedwith permission from Quinlan P, Nummikoski P,
SchenkR. Immediate and early loading of SLA ITI
single-toothimplants: an in vivo study. Int J Oral Maxillofac
Im-plants. 2005 May-June;20(3):360-70.19
Figure 13. Loading documentation in the literature foredentulous
mandible. Reprinted with permission fromCochran DL, Morton D, Weber
HP. Consensus state-ments and recommended clinical procedures
regardingloading protocols for endosseous dental implants. Int
JOral Maxillofac Implants. 2004;19 Suppl:109-13.21
Figure 14. Loading documentation in the literature foredentulous
maxilla. Reprinted with permission fromCochran DL, Morton D, Weber
HP. Consensus state-ments and recommended clinical procedures
regardingloading protocols for endosseous dental implants. Int
JOral Maxillofac Implants. 2004;19 Suppl:109-13.21
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162 Cochran June 2006
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bone surrounding the implant with resultant secondary
bonecontact. These conditions result in 2 clinical scenarios
forsupporting reduced healing times. If the implant site has
highquality and quantity of existing bone, immediate loading
pro-tocols are possible. If the implant site has low quality
andquantity of native bone and bone remodeling and boneformation
are required, immediate loading is more contra-indicated and early
loading protocols are possible. However,many factors can be
important such as the characteristics ofthe implant surface, the
location of high-quality bone in theimplant site, the ability to
protect the implant restoration withadjacent tooth structure, the
use of proteins (growth factorsor stimulants) or materials and
matrices used around theimplant, and so forth. These factors are
related to either (1)stimulating new bone-to-implant contact or (2)
minimizingmicromotion of the implant. In all situations, it is
impor-tant to remember that the goal is improved patient
care.Procedures that put the implant restoration at high risk inthe
patient are unacceptable. Understanding the historicaldevelopment
of implant healing times, the biological eventsthat result in
osseointegration as defined above, and knowingthe literature on
shortened healing times on implants, allowsthe clinician to
appreciate options for various loading pro-tocols and to improve
the patient care they deliver.
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24. Morton D, Jaffin R, Weber H-P. Immediate restoration and
loading ofdental implants: clinical considerations and protocols.
Int J Oral Maxil-lofac Implants 2004;19(Suppl):103-8.
Figure 15. Loading documentation in the literature forpartially
dentate maxilla and mandible. Reprinted withpermission from Cochran
DL, Morton D, Weber HP.Consensus statements and recommended
clinical proce-dures regarding loading protocols for endosseous
dentalimplants. Int J Oral Maxillofac Implants. 2004;19
Suppl:109-13.21
JOURNAL OF EVIDENCE-BASED DENTAL PRACTICE
Volume 6, Number 2 163Cochran
The Evidence for Immediate Loading of
ImplantsINTRODUCTIONHISTORICAL PERSPECTIVEBIOLOGICAL
CONSIDERATIONSLITERATURE EXAMPLESCONCLUSIONReferences