GOOD AFTERNOON

IMPLANT LOADING PROTOCOLS AND THEIR RATIONALE

Sushant Rohilla Junior Resident III

INTRODUCTIONPredictable formation of a direct bone to

implant interface is a basic treatment goal in implant dentistry.

The TWO STAGE SURGICAL PROTOCOL for implant placement and prosthodontic rehabilitation as established by Branemark et al. (1977) to accomplish osseointegration consist of several prerequisites, which include -

• Countersinking of the implant below the crestal bone.

• Obtaining and maintaining a soft-tissue covering over the implant for 3 to 6 months.

• Maintaining a minimally loaded environment for 3 to 6 months.

The primary reasons cited for submerged, countersunk surgical approach to implant placement were –

• To reduce and minimize the risk of bacterial infection,

• To prevent the apical migration of the oral epithelium, and

• To minimize the early implant loading.

Branemark and several other workers achieved predictable long term, clinical rigid fixation with this protocol both in partially and completely edentulous patients.

However there are some drawbacks related to this type of classical loading protocol .

DRAWBACKS OF BRANEMARKS’

LOADING PROTOCOL

• Discomfort and inconvenience of second stage surgery.

• Extended treatment time.

• It was observed that even if an initial direct bone to implant interface has been established and confirmed at post healing stage II surgery, the implant is most at risk for failure or crestal bone loss within the FIRST YEAR.

If the treatment provides adequate support,the three most common causes of early prosthetic related implant failure are –

• Non passive superstructure,

• Partially unretained restorations, and

• Loading of the implant support system beyond the strength of the bone to implant interface.

Challenging the very concept of Branemark , came two different protocols for loading of implant- bone interface –

PROGRESSIVE IMPLANT PROGRESSIVE IMPLANT LOADINGLOADING ANDAND IMMEDIATE IMPLANT IMMEDIATE IMPLANT LOADING LOADING PROTOCOLSPROTOCOLS

Misch (1980) proposed the concept of progressive or gradual bone loading during prosthetic reconstruction to decrease the crestal bone loss and early implant failure in endosteal implants.

Progressive bone loading is more critical for lesser bone densities because they are several times weaker than the those with significant cortical bone.

PROGRESSIVE IMPLANT LOADING

Parafunction, cantilever and other stress magnifiers can increase the force applied to the prosthesis and their shear components and cause bone microfracture or microstrains in the pathologic loading zone .

The ULTIMATE AIM OF PROGRESSIVE BONE LOADING is to

increase the density of bone, decrease the risk of implant-bone failure decrease crestal bone loss

As per the WOLFF’S LAW ( 1892) “ Every change in the form or function of bones or of their function alone is followed by certain definite changes in their internal architecture and equally definite alterations in the external conformation, in accordance with mathematical laws.

BONE DENSITY IN RELATION TO PROGRESSIVE LOADING

Generalized loss of bone volume and density occurs in regions of tooth loss. The decrease in density is related to-

Length of edentulismOriginal density of the boneMuscles attachmentsBone flexure and torsionParafunction Hormonal influencesSystemic conditions

Bone responds to hormonal and biomechanical regulation and even in conditions with high demands calcium, functional loading can compete and maintain bone mass (Marks et al.1988).

Bone also responds to stress if within physiologically limits and exercise prevents bone loss.

Frost showed that increase in bone mass is related to strain applied to the bone . The actual strain perceived by the bone tissue initiates a chain reaction of events that results in biological response .

BONE CELLS and EXTRACELLULAR MATRIX compose the strain sensitive population.

Membrane deformation, intracellular action, and extra-cellular action are proposed cellular mechanisms.

Dynamic or cyclic loading is necessary for boneremodeling.Greater the rate of change of applied strain in

bone , the more bone formation is increased.Lower magnitude for many cycles can produce

the same anabolic effect that a greater magnitude force applied force will produce if applied for shorter durations.

Functional loading of implants brings biomechanical influences, which greatly affects the bone maturation.

Bone density increase is primarily reflective of the local stress factors and endosteal implants are major methods to alter the strain and increase the bone density.

BONE IMPLANT INTERFACE

The ideal bone for the implant prosthetic support is LAMELLAR BONE, which is highly organized but takes 1 year to mineralize completely after surgical trauma induced by the implants.

WOVEN BONE is the fastest and first bone to form around implant interface, however it is only partially mineralized / organized and less able to withstand full scale stresses.

At 16 weeks ( 4 months) after implant placement, the bone is only 70% mineralized and of woven bone nature.

The greatest stress around a rigidly fixated implant occurs at the bone crest.

According to Manz, the crestal bone loss after successful bone integration was related to directly to the bone density.

As bone is loaded physiologically , a gradual increase in loads during prosthesis fabrication stimulates an increase in bone density.

It was further observed that softer bones lost more of crestal bone , and increasing the bone implant interface density reduce the crestal bone loss.

• It is well agreed fact that fewer the no. of implants, softer the bone type, and higher the risk factors ( eg. presence of cantilevers, patient force factors, implant position etc) , more critical will be the progressive bone loading.

PROGRESSIVE LOADING PROTOCOL

• Full arch prosthesis with little or no cantilever , adequate implant no, position, and size rarely require progressive implant loading.

• The favorable biomechanics of an arch are compatible with immediate loading protocol.

• The principles of progressive loading are demonstrated best in cement retained prosthesis and are least applicable for screw retained bar of a mandibular removable prosthesis ( RP-5).

• Screw retained prosthesis are difficult to load progressively because-

a) Transitional prosthesis is movable during fabrication phase.

b) Most of the forces placed on to the implants are generated a delivery due to non passive superstructure.

Generally longer healing time are suggested if force kevels are greater

(a)TIME Branemark’s two stage protocol separates initial

implant placement and stage II uncovery by 3 to 8 months.

• In Progressive loading protocol usually five major prosthodontic appointments are made and are separated by some specific time interval related to bone density observed at the initial surgery.

In addition the dentist attempts to gradually increase the loading to the implants at each prosthetic step.

• Macroscopic coarse trabecular bone heals about 50% faster than dense cortical bone.

• D1 bone heals slowest but is strongest and has greater lamellar bone contact.

• D3 and D4 bones are suggested to have greater healing time ( 5 and 6 months resp.) because of lesser bone contact and decreased amount of cortical bone to develop same levels of interface maturation. So it further seems that progressive loading is more critical of these type of bones.

b) DIET The dentist controls the diet of the patient to

prevent overloading during the early phases of the restorative process .

• DURING THE INITIAL HEALING PHASE, The dentist instructs the patient to avoid

chewing in the area of the implant placement. Once uncovered, the implant connected to high

abutment is at greater risk of loading during mastication.

• FROM THE INITIAL TRANSITIONAL PROSTHESIS DELIVERY UNTIL INITIAL DELIVERY OF THE FINAL PROSTHESIS

The patient is limited to soft diet. Masticatory force limit is 10psi. The soft diet not only minimizes the

masticatory force on the implants and thus overloading of implants but also decrease the risk of temporary restoration fracture or partially uncemented restoration.

• AFTER THE INITIAL DELIVERY OF THE FINAL PROSTHESIS ,

The patient may include slightly tougher diet (meat) Masticatory force limit is 21 psi.

• AFTER FINAL EVALUATION APPOINTMENT The patient may include raw vegetables which

requires a masticatory force of 27 psi .

• A NORMAL DIET IS PERMITTED ONLY AFTER EVALUATION OF THE FINAL PROSTHESIS FUNCTION, OCCLUSION AND PROPER CEMENTATION

c) OCCLUSAL MATERIAL The occlusal material may be varied to load

the bone to implant interface gradiually.

• During the initial steps t he implants has no occlusal material over it .

• At subsequent appointments, the dentist uses acrylic as the occlusal material, with the benefit of lower impact force than the metal or porcelain.

• As a final restoration,either metal or porcelain can be used.

• If parafunction or cantilever length cause concern relative to the amount of force on the early implant-bone interface, the dentist may extend the softer diet and acrylic restoration phase several months. In this way, the bone has a longer time to mineralize and organize to accommodate the higher forces

d) OCCLUSIONThe dentist gradually intensifies the occlusal

contacts during prosthesis fabrication.

• No occlusal contacts are permitted in initial healing time ( step1).

• The first transitional prosthesis ( step 2) is left out of occlusion in partially edentulous and no cantilever are made in transitional prosthesis of edentulous patients

• At transitional prosthesis stage II appointment (step 3),the occlusal contacts then are similar

to those of final restoration for areas supported by implants, however occlusal contacts are avoided on cantilever. The occlusal table is kept narrow like in final restoration.

• The occlusal contacts on final restoration follows implant protected occlusion guidelines and occlusal table is kept narrow.

e) PROSTHESIS DESIGN

• DURING INITIAL HEALING PHASE The dentist attempts to avoid any load on the

implants, including soft loads.

• The FIRST TRANSITIONAL ACRYLIC RESTORATION in partially edentulous patients has no occlusal contacts and no cantilevers. The main purpose of this is to splint the implants together, to reduce stress by the mechanical advantage, and to have implants sustain masticatory forces solely from chewing

• In the SECOND ACRYLIC TRANSTIONAL RESTORATION occlusal contacts are placed on the implants with occlusal tables similar to the final restoration bust with no cantilever in non-esthetic regions.

• In the FINAL RESTORATION, narrow occlusal tables and cantilever are designed with occlusal contacts following implant-protective occlusion guidelines

• Fig 26-5

During the last 18 years several authors have reported that root form implants may osseointegrate, even though they extend above the bone and through the soft tissues during early bone remodelling.

This surgical approach has been called a ONE STAGE or NONSUBMERGED IMPLANT PROCEDURE because it eliminates the second stage implant uncovering surgery.

IMMEDIATE IMPLANT LOADING

• Immediate loading not only includes a non submerged one stage surgery but actually loads the implant with the provisional restoration at the same appointment or shortly thereafter.

• Immediate loading is not new but was the initial protocol suggested with dental implants.

RATIONALE OF IMMEDIATE IMPLANT LOADING

The immediate load concept eliminates the second stage surgery and thus the resultant discomfort and inconvenience of , and the time required by the surgery and suture removal process.

In addition splinted implants could decrease the risk of overload to each implant because of greater surface area and improved biomechanical distribution .

• The patient does not need to wear e removable restoration during initial bone healing which greatly increases comfort, function , speech and stability and enhances certain psychological factors during transitional period.

• Over the last few years several authors have reported on immediate loading in completely edentulous patients, with 95-100% success rate

a) SURGICAL TRAUMA • Surgical process of implant insertions causes

regional accelerated phenomenon of bone repair around the implant interface.

• As a consequence of surgical placement, lamellar bone in preparation site becomes woven bone of repair next to the implants.

• Woven bone forms at a rate upto 60 MICRONS PER DAY as compared to lamellar bone which forms at rate upto 10 MICRONS PER DAY.

• At 16 weeks ( 4 months) the surrounding bone is still only 70% mineralized and exhibits woven bone as a component.

• The IMMEDIATE IMPLANT LOADING CONCEPT challenges the conventional healing time of 3 to 6 months of no loading before the restoration of the implant.

Often the risks of this procedure are perceived to be during the first week after the implant insertion surgery. In reality, the bone in the macroscopic thread design is stronger on the day of the implant placement compared with the 3 months later, since there is more mature lamellar bone in the threads in the implant

Early cellular repair is triggered by the surgical trauma and begins to form an increased vascularization and repair process to the injured bone.

Woven bone formation may start at 2nd week after implant placement. And the bone implant interface is at highest risk of overload failure at 3-5week after implant placement.

• Reduction of surgical trauma in an effective method to have more vital bone at the implant- bone interface ( Roberts1984, found 1 mm wide zone of devitalized bone at interface) which reduces the risk of immediate occlusal overload .

The main causes of surgical trauma are THERMAL and MECHANICAL TRAUMA.

* Temperature next drill --- 38’C to more than 41’C base line and required 34 to 58 seconds to

return to baseline

• Drills with internal cooled system drill at higher temperature than those with external irrigation.

• Drill rpm of 2500 produce less heat than 2000 rpm, while 1250 rpm produced created most heat.

• Factors related to heat production are- - amount of bone prepared - drill sharpness - depth of osteotomy - variation of cortical thickness - temperature and solution chemistry of irrigatant.

• The implant bone interface will have a larger zone of repair when the implant is significantly compressed against the bone. Eg a self tapping implant may cause greater bone remodeling compared with a bone tap and implant placement technique.

• The implant should not be mobile at placement but excessive stress should be avoided. For immediate loading implant placement within the bone is limited to 45-60 Ncm

• Reverse torque test of 20 Ncm is used to evaluate the quality of bone and interface fixation ( Sullivan 1996, Palti 2002).

If implant does not unthread at 20Ncm the resistance indicates that the bone is of sufficient density to consider immediate loading.

b) BONE LOADING TRAUMA Once the bone is loaded by an implant prosthesis,

the interface begins to remodel again but the trigger now is STRAIN TRANSFER CAUSED BY OCCLUSAL FUNCTION, rather than the trauma of implant placement.

The woven bone thus formed may be called REACTIVE WOVEN BONE , and the remodeling is called BONE TURNOVER.

INTERFACE REMODELING RATE is the period of time for the bone at implant interface to be replaced with new bone

• When the surgical trauma is too great or the mechanical trauma situation is too severe, fibrous tissue may form rather bone, resulting in clinical mobility.

FACTORS WHICH REDUCE RISK IN IMMEDIATE LOADING PROTOCOL

The factors are –1. BONE MICROSTRAIN2. INCREASED SURFACE AREA a) implant no. b) implant size c) implant body design d) implant surface condition

3. DECREASED FORCE CONDITION a) patient conditions b) occlusal load direction c) implant position

4. MECHANICAL PROPERTIES OF THE BONE

1. BONE MICROSTRAIN Microstrain levels 100 times less than ultimate strength of bone may

trigger a cellular response. The ideal microstrain for bone is called PHYSIOLOGICAL / ADAPTED ZONE - 50 TO 1500 microstrain and is IDEAL LOAD BEARING ZONE

• One goal for an immediate loaded implant/ prosthesis system is to decrease the risk of occlusal overload and its resultant increase in the remodeling rate of bone.

Under these conditions the surgical regional acceleratory phenomenon may replace the bone interface without the additional risk of biomechanical overload.

• If occlusal overload is not managed it will result in 1500 – 3000 microstrains that is mild overload zone causing trauma from overload. And will hamper the bone remodeling from surgical trauma.. Laeding to bone being less mineralized, less oraganized, weaker, and lower mod. of elasticity.

2. INCREASED IMPLANT SURFACE AREA a) IMPLANT NUMBER When immediate loading protocol is used

increased no. of implants are of special importance because-

- It increases the surface area - Increases the success rate even if one or two

implants fail. - Increases the retention of prosthesis - Reduces the no. of pontics

• Often more implants are used in maxilla ( 8-10) than mandible (5-9), which compensates for less dense bone and increased directions of force found in upper arch.

b) IMPLANT SIZE Implant height is not an effective method to

decrease stress, as far as non-immediate implant loading proto is considered, because it doesn't address the problem in functional surface area region of bone-implant interface, which is better related to implant width and design

However because the implant is loaded before the establishment of histologic interface and implant height is important for initial stability of implant , IMPLANT HEIGHT IS MORE RELEVANT FOR IMMEDIATE IMPLANT LOADING applications, especially in softer bones.

c) IMPLANT BODY DESIGN

The implant design should be more specific for The implant design should be more specific for immediate loading because the bone has not immediate loading because the bone has not had time to grow into recess or undercuts , had time to grow into recess or undercuts , attach to surface conditions before application attach to surface conditions before application of occlusal load.of occlusal load.

Threaded implants allow bone to be present in depth of threads from the day of insertion as compared to

press fit design.

Greater the no. of threads, greater the functional surface area at the time of

immediate load

Greater the thread depth greater the surface area for immediate load applications

• Functional surface area of an implant may affect the remodeling rate of the bone during loading. An implant with less surface area have more remodeling rate, and higher the remodeling rate, weaker the bone interface.

Square threads show better resistance to torque than V shaped or reverse buttress design.

• TAPERED DESIGN PRESENTS DISADVANTAGES FOR IMMEDIATE LOADING APPLICATIONS

- They do not engage the bone physically as nicely as parellel , reducing the intial fixation.

- Along with this they have lesser total surface area, lesser thread depth and no.

- They engages lateral cortical plate to lesser extent at the apical region, and any de-rotation may lead to lesser fixation.

d) IMPLANT SURFACE CONDITION • Surface conditions the rate if the bone

contact, lamellar bone formation, and the % of bone contact.

• The surface condition that allows bone formation in greatest percentage, higher bone implant contact % with higher mineralization rate, and fastest lamellar bone formation would be of benefit to immediate loading protocol.

• Hydroxypatite (HA) has been shown to have these properties along with reduced rate of bone remodeling during occlusal loading.

• Hence if bone is not of ideal density (D4) for immediate loading HA may decrease risk of overload.

3. DECREASED FORCE CONDITION The dentist should reduce the factors that

magnify the noxious effects of force factors in terms of magnitude, duration ,type and direction

a) PATIENT FACTORS Force factors increase the risk for immediate

loading. Parafunction such as bruxism and clenching not

only leads to increased force but also the duration , more horizontally directed forces.

.

Parafunction also increases the risk of abutment screw loosening, unretained restoration, and restoration fracture , jeopardizing the load distribution on immediate loaded implants

b) OCCLUSAL LOAD DIRECTION Axial load maintains the lamellar bone and has lower

remodeling rate than horizontally directed loads. Therefore cantilevers in posterior regions should be avoided

in immediate loaded implant’s transitional restorations

C) IMPLANT POSITION Cross arch splinting is an effective design to reduce

stress to entire implant support system, especially in completely edentulous patients rehabilitated with immediate loading.

Mandible may be divided into three sections : canine to canine area, and the bilateral posterior

sections.

In mandible cross splinting has been an issue of debate because of flexion and torsion distal to mental foramen, but clinical reports show that acrylic resin transitional prosthesis can solve this problem.

However final restoration must be made in three sections described.

• Maxilla require more implant support than mandible because or less dense bone and direction of of forceoutside of the arch in all eccentric movements.

• Maxilla is divided in to 4 or 5 sections depending on force conditions and arch shape.

Minimum four sections are bilateral canine regions and bilateral posterior regions.

• When force factors are high , the incisor region is included along with the standard four sections.

At least one implant should be inserted into each maxillary section and splinted together during the immediate loading applications.

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