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2 Implant vs Tooth: Biomechanics

2 Implant vs Tooth: Biomechanics

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15  Implants in the Aesthetic Zone: Occlusal Considerations



Table 15.1  Summary of biological and biomechanical factors influencing the occlusion of dental

implants

Biological/

biomechanical

factors

Periodontal

ligament (PDL)

Nervous

innervation



Compressive

forces (axial

forces)

Shearing forces

(excursive

movements)



Tactile sensitivity



Tooth

A vital tissue surrounding the tooth. It

attaches the tooth to the bone. It offers

cushioning effect and repair to protect the

tissue from trauma

PDL is innervated by nerve endings which

are sensitive to pressure, called

mechanoreceptors. These act as feedback

source for pain sensation due to excessive

occlusal force

Due to resilience of the PDL, a tooth can

be compressed to about 25–100 μm in the

socket

Horizontal movements due to shearing

forces are 50 μm

Elasticity of the tooth makes it invulnerable

to subtle bending moments caused by

excursive movements



Implant

There is no such peri-implant

specialized tissue present

Peri-implant nerve

innervation is present, but it

is not as specific and as dense

as around a tooth

An implant can be

compressed only 3–5 μm



Horizontal movements due to

shearing forces are 10–50 μm

Rigidity of the implant

makes it vulnerable to

bending moments caused by

excursive movements

Due to high innervation of nervous tissue, a Due to low innervation of

force as low as 0.3 N can be detected

nervous tissue, a force of at

least 15 N can be detected



movement is not linear. It begins with an initial phase, where the tooth moves

within the boundaries of the PDL [14]. Continued force involves the secondary

phase, which involves elastic deformation of the alveolar bone. In contrast, the

implant lacks an initial, adaptive phase of movement. The implant moves (<50 μ)

in a linear and elastic fashion (Table 15.1).



15.3 Consequences of Overloading

Occlusal overload has been implicated as one of the contributing factors for atypical peri-implant bone loss. Theoretically, this is possible though unproven. As

previously mentioned, the stress distribution of an implant occurs at the crestal

bone level. The difference in the elasticity modulus of bone compared with that of

the titanium implant suggests that forces are directed to the first area of boneimplant contact (BIC), the crestal bone. Microfractures in this area could in turn

produce marginal bone loss. Conclusions from the best available literature are

varied: ranging from a possible association, a possible relationship including

other factors, to no probable association. Proper clinical trials are needed in this

area to determine a conclusive link between occlusal overload and atypical periimplant bone loss.



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R. G. Stevenson III and A. Agnihotry



In a small animal study, Kozlovsky et al. [15] found that dynamic occlusal overload created marginal bone loss; however, the extent of the bone loss was determined by the presence of ligature-induced inflammation. Without inflammation, the

bone resorption did not occur below the implant neck with “overloaded” implants.

The presence of plaque-induced inflammation led to significantly greater bone loss.

Clinicians have theorized that, if occlusal overload is indeed associated with marginal bone loss, the micro-movements could lead to the development of

peri-implantitis.

Similar controversy surrounds a possible association between occlusal overload

and the loss of osseointegration. There is no high-quality evidence on the relationship between osseointegration and supraoccluded implants in humans, and the

available animal studies contradict such association in healthy conditions [16].

However, animal studies have shown that occlusal overload (mimicked by supraocclusal contacts with inflammation) increases the plaque-induced bone resorption

quite significantly [16].

Still, there are some cases reported with bone loss attributed to overloading in

dental implants [17–20]. These mixed results can be attributed to complicated

nature of studying occlusal overload in a clinical setting. In light of the incomplete

and inconclusive evidence, let us deal with occlusal overload by a precautionary

principle. Because, even if overloading only leads to biomechanical complications

(screw loosening, prosthesis failure, and the fracture of screws, veneering material),

or failure of the implant, it can be costly and time-consuming to restore them back

to optimal form and function.



15.4 Dynamic Occlusion: Function

Although the use of an articulator is indicated for oral rehabilitations and is particularly important for implant restorations, one must come to terms with the fact that the

articulator, no matter how sophisticated, is not a reliable device capable of replicating

the patients’ actual function [21]. The properly adjusted articulator is essential to

establish the anterior occlusal plane for aesthetics, phonetics, pathways of the planned

guidance to decrease forces and protect posterior teeth from untoward lateral forces,

posterior cusp heights to enhance chewing efficiency while reducing interferences,

anterior lingual anatomy, and inclination angles to coordinate with the condylar guidance and posterior cusp inclines, and it serves to allow the technician the ability to

create restorations that may be transferred to the mouth with minimal modifications

and adjustments. A properly adjusted articulator is indispensable to be sure; however,

the actual occlusal function of the patient, chewing, speaking, swallowing, and respiration, cannot be accurately or precisely predetermined with the use of an articulator.

After following the well-known principles of occlusion on the articulator, it is

critical to be able to determine the dynamic occlusion of the patient—that is, that

actual pathways and patterns exhibited by the patient. We will discuss and describe

the practical steps which will provide the clinician with a plan for anterior implant

restoration delivery.



15  Implants in the Aesthetic Zone: Occlusal Considerations



301



15.5 O

 cclusal Considerations in History, Examination,

and Treatment Planning

15.5.1 Acceptable Occluding Surfaces and Relationships

1. Bilaterally stable and uniform posterior occlusal contacts in MIP, with the anterior teeth not making any contact unless the individual squeezes.

2. Absence of occlusal trauma to the dentition, which may be indicated by: pain in

the individual tooth; a widened PDL with increased mobility, root resorption,

cementum resorption, alveolar bone changes, pulpitis, tooth/restoration fractures, or a combination of these conditions.

3. Absence of tooth structure loss from occluding surfaces. In vivo studies have

confirmed that occlusal wear of natural enamel opposing natural enamel is

approximately 15–17 μ in the premolar region and twice that (29–35 μ) in the

molar region per year (Table 15.2) [22, 23].

4. Wear that exceeds these amounts on the tooth-tooth, tooth-restoration bearing

interfaces or is isolated indicates attrition (tooth-tooth) or abrasion (tooth-­

restoration). However, erosion (corrosion) from intrinsic or extrinsic factors

must be ruled out or treated accordingly. Simply diagnosing wear as parafunction is an incorrect and incomplete diagnosis. It lacks a specific diagnosis which

will require a specific treatment protocol. Fabricating night guards for any individual with wear is not an appropriate treatment. Anecdotally, the authors have

seen patients with obvious erosion from undiagnosed and untreated GERD (possibly associated with sleep disorders) treated with occlusal splints, without any

improvement in their progressing condition.

5. Absence of non-axial loading or tooth migration. If diastema is developing, particularly over the recent years, this is an indication that occlusal forces are currently overloading the normal tooth positions which is further exacerbated by the

lack of bone support, posterior occlusal support, and mobility due to advanced

periodontitis [24, 25]. Placing dental implants in patients with active periodontal

disease negatively affects long-term success [26, 27]. Placement of implants in

these patients, without stabilizing the posterior dentition and controlling the

active disease process, is contraindicated.

6. Absence of anterior and posterior occlusal plane discrepancies. If the anterior and

posterior occlusal planes are not symmetrical and uniform in anteroposterior, sagittal, and frontal planes, this is not only an aesthetic issue but an occlusal discrepancy as well. Attention must be given to understand these discrepancies and treat

them with orthodontics and/or maxillofacial surgical interventions, if needed for

optimal results, as part of an overall treatment strategy.

Table 15.2  Normal occlusal wear with advancing age based on documented evidence

Age

Amount of tooth loss first molar (mm)

Amount of tooth loss premolar (mm)



30

0.72

0.27



40

1.02

0.42



50

1.32

0.57



60

1.62

0.72



70

1.92

0.87



80

2.22

1. 02



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R. G. Stevenson III and A. Agnihotry



15.5.2 Acceptable Occlusal Vertical Dimension (OVD)

The OVD cannot be corrected in most cases without an impact on the amount of

display of the anterior teeth while at rest (repose) and smiling. Although OVD corrections may be indicated due to loss of tooth structure in the posterior teeth, it is

incumbent on the clinician to determine what effect this will have on the anterior

component of the teeth with respect to aesthetics. There are numerous instances

where the OVD simply cannot be corrected without creating unwanted or unnatural

display of the anterior teeth. The desire to correct the OVD to improve the occlusal

pathways and occlusal planes may need to be considered more carefully prior to

initiating a major reconstruction. It may create a more ideal occlusion, however,

with undesirable aesthetics. It is important to note that for most patients, they are

driven by aesthetics, not occlusion. The clinician must consider a reconstruction

focused on facial aesthetics and work from this when considering functional (occlusion), biomechanical (structural), and periodontal treatment planning.



15.5.3 Acceptable MI Position (MIP) and Centric Occlusion (CO)

Very few individuals will have an MIP coincident with the condyles in a fully seated

position (centric relation). An occlusal slide from the first point of contact (centric

occlusal contact) to MIP of <2 mm with intact proprioception is acceptable for the

vast majority of patients. A CR-MIP slide only becomes an issue when it is large or

when the patient develops symptoms which make the MIP position unacceptable. In

such instances, further diagnostic tests are indicated, including a comprehensive

TMJ examination, muscle testing, and centric relation mounting/evaluation of casts.

The use of deprogrammers (anterior bite planes) and monitoring of symptoms are

critical to obtain a stable and pain-free position of the joints and teeth. The treatment

may include occlusal equilibration/restorations in cases of occlusal dysfunction and

orthodontics/surgery/rehabilitations in cases where movements of the anterior teeth are

constricted (constricted chewing patterns or constricted envelopes of function) [28].

Preferably centric occlusion and MIP are coincident; in other words, when the

jaws are in the superior midmost and anterior braced position (CR), the teeth are

able to achieve a comfortable MIP.  When altering occlusal vertical dimension

(OVD), or treating cases of occlusal dysfunction, this is a primary objective of

achieving a stable (and successful) occlusion.



15.5.4 Occlusal Schemes [Acceptable Anterior Guidance (AG) or

Group Function (GF)]

Single Tooth Implant

• Incisors: To maintain good contacts and a suitable emergence profile, light contacts on the marginal ridges are acceptable in maximum intercuspation (MIP),

with little or no contacts with protrusive movements.



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