Transfer of Maxillomandibular Relationship From

¶ … transfer of maxillomandibular relationship from patient's mouth to articulator is one of the most essential procedures in the prosthodontic. There are important skills and techniques that should be followed and applied by clinicians as well as lab technicians to obtain accurate and precise restoration either without or with minimum occlusal adjustment upon cementation. In addition to that, the muscles of the jaws might change in length and affects the patient's bite. On the other hand, patients might bite in different positions than his normal bite due to lack of enough instructions and guide. The bite registration has been reported in the literature with some controversy, and this is due to multiple variables related to the technique, the material used, the patient, the technician, or the dentist.

This paper will review the literature, to describe and evaluate the important variables to produce an accurate bite Registration. This will help in providing easy delivery and cementation of prosthesis and restorations, with minimal occlusal adjustment upon cementation and insertion in the patient mouth.

2-Introduction:

Owen defines occlusion as, "The static relationship between the incising and masticatory surfaces of the maxillary or mandibular teeth or tooth analogues." In addition, he illustrates the significance of Occlusion, "Occlusion has been described as the most important subject in all the disciplines of dentistry, and for good reason, because the way the teeth come together, and function together, is as important to most of us now as it was to our ancestors, who lived on diets much more difficult to cope with. When, as dentists, we are faced with the problem of replacing occlusal surfaces, either by restorations in natural teeth, or replacement of some or all of the teeth, then a thorough knowledge of the way teeth come together and function together, is essential."

He further illustrates, "Occlusion has unfortunately also been described as one of the most confusing subjects in all the disciplines of dentistry (mostly by each generation of dental students). Attempts to understand occlusion have ranged from the mechanical, mathematical and geometrical analysis of tooth contact and jaw movement, to the biological and functional analyses based on the behavior of natural dentitions under different environmental (mostly dietary) conditions. All of these analyses have their place but they need to be brought together into a unified concept, and this is rarely done."

As mentioned above, occlusion can be considered to be one of the most significant factors in dentistry for the reason that the success of dental treatment relies very heavily on the relationship between maxilla and mandible. Dental occlusion or the maximum intercuspation as it is known is the normal spatial relation of the teeth when the maxilla and mandibular jaw come together in contact. However there are three factors that affect occlusion, teeth, muscles and tenpromandibular joint, all working together to produce the best bite possible. Dental Practitioners nowadays are challenged to provide reliable bite registration that register correct occlusal relationship between maxilla and mandible during construction of Fixed partial denture and Removable prosthesis (Warren and Capp, 1990).

Few years back, the most common problem encountered by the prosthodontists and general dentists is ill-fitting dental restorations. When they receive the fabricated restoration from dental laboratory technician most of them are with high occlusal contact, the dentist spend several minutes in adjusting the prosthesis in the patient mouth. The restoration fitting nicely on the master casts on the articulator, and that was according to the bite registration which did not duplicate the jaws relation in proper position. Dentist usually blame the dental technician for that ill-fitting restoration, however he is the one who register the bite wrongly. In fact, review and follow up of the patients cooperation, muscle dysfunction, centric relation, centric occlusion, occlusal vertical dimension, temporomandibular joint status, these factors are the basic principles in obtaining the accurate bite registration (Warren and Capp, 1990).

Lack of proper bite registration may affect function, stability, aesthetics and the overall comfort of the prosthesis. Achieving a correct bite registration create an occlusal scheme that allows the patient to move through the full range of functional movement without interference. The type of occlusal relationship selected, articulator, bite registration technique are important in achieving proper bite and successful prosthesis (Warren and Capp, 1990).

The most common errors found due to improper bite registration are improper vertical dimension, lacking stability in centric occlusion, and occlusal interferences in eccentric movement. In addition to improper prosthesis lab work, some of the dentists have inadequate information and skills to register their patients' bite properly, especially for complex and comprehensive cases with missing multiple missing posterior teeth. Patients needs occlusion reconstruction, whether it is removable prosthesis or fixed partial denture will require more time in the clinic to achieve accurate bite registration and interocclusal record materials with minimal dimensional change in order to record precise maxillomandibular relation (Warren and Capp, 1990).

3-Aims of this paper:

To determine and discuss all the important points in registration of an accurate interocclusal relationship for fabrication of prosthesis and to keep away dental practitioners from massive adjustment upon cementation and chair side insertion of the prosthesis.

3.1-Objectives:

The achievement of this paper is to minimize the error produced during interocclusal record:

1-

Identify the causes that affect an accurate bite registration in prosthodontics.

2-

Enhance of knowledge of understanding on the proper ways to recording bite registration.

3-

Discus the importance of Articulator selection.

4-

Discus how variables of occlusion among patients affect the restoration of a posterior tooth.

5-

Identify the muscle role in bite registration.

4-Basic principles:

Before starting the bite record there is some essential factors and techniques should be followed and evaluated from the clinician and dental lab technician to obtain the accurate restoration with a successful occlusal contact that include:

1.

Tmpromandibular joint and Muscles

2.

Centric occlusion

3.

Centric relation.

4.

Occlusal Vertical dimensional.

4.1-Centric occlusion:

4.1.1-Definition:

As mentioned above, occlusion, in the context of dentistry refers to the manner wherein the upper teeth and the lower teeth of a patient join and meet together. At first, Occlusion was described as the manner wherein each tooth in the mouth joined its counterpart in the opposite arch. Centric occlusion can be defined as the position of teeth when they come together in maximum occluding intercuspation according the normal patients bite (Davies and Gray, 2001). Dawson said this term is used when the occlusal surfaces of both maxilla and mandibular fit together in maximum contact regardless of condylar position (Dawson, 1974). Another author defined centric occlusion as long centric occlusion, when the lower teeth are in maximum contact with the upper teeth and the lower jaw can move freely 1 to 1.5 mm anteriorly (Christensen, 2004). In addition, Owen defies centric occlusion as, "The occlusion of opposing teeth when the mandible is in centric relation. This may or may not coincide with maximum intercuspation."

So in short, centric occlusion is a concept that is used to illustrate the location of the lower jaw at the time when the upper and lower teeth are completely occluded (joined). This differs from one person to another as it relies on both the number as well as the position of teeth in both jaws. In the figure below, all 32 teeth are not only present but they are also occluding (i.e. biting) in a relationship referred to as class I. This, however, can alter at any point in time in an individual's life as this relies on issues such as:

1. The teeth/tooth being lost (and the subsequent shifting of the teeth that occurs after teeth have been cut off),

2. Jaw-line fractures,

3. Teeth's orthodontic shifts to newer locations, or

4. The teeth movement because of the continuous force from bruxing.

When the upper and the lower teeth are completely occluded, the condyle is pressured to move into a precise location inside the "glenoid fossa." It should be noted here that the concept "centric occlusion" does not take into consideration the joint configuration. An individual's centric occlusion might be either physiologic or pathologic. Physiologic centric occlusion means that the upper and the lower teeth are positioned in a very comfortable location. Pathologic centric occlusion means that the upper and lower teeth are forced in an eccentric location that might generate dysfunction of the joints (Sharry, 1973).

4.1.2-mechanism and philosophy of the centric occlusion

In the normal occlusion the upper and lower teeth contact in the maximum intercuspation and both condyle are comfortably seated in the gelenoid fossae without any interference (see figure 1). It should be noted here that in nearly ten percent of the population the centric occlusion coincides with the centric relation (Rosenstiel and Land, 2001). This means that the force acting on both the upper and lower teeth ought to be distributed equally to generate teeth stabilization. Furthermore the maximum intercuspation depends on the number of posterior teeth present along with the tempromandibular joint (TMJ) and canine guidance (Dawson, 2007; Rosenstiel and Land, 2001).

Figure 1:

The TMJ is the ball as well as the socket joint that permits the lower teeth set to both open as well as close. The understanding of TMJ anatomy as well as its function is very important to generate stable as well as healthy intercuspation. TMJ consists of condyle, disk, muscles and ligaments. It connects the lower jaw to the temporal bone in the skull in both sides and has two movements (Rosenstiel and Land, 2001). The TMJ along with muscles stabilization is the starting point to get the ideal maxilla-mandibular relationship in the centric relation. There is no way to register and transfer an accurate interocclusal record if patient has TMJ or muscles dysfunction. The patient with this dysfunction should be treated first before final restoration, cementation or construction. The conservative management of unstable joints and muscles via appliance therapy is the most common modality of management (Capp and Clayton, 1985).

4.2 Occlusal vertical dimension:

Perhaps one of the toughest and most intricate recuperative experiments for dentists in today's world is directly related to the occlusal vertical dimension (OVD). However, dentists have realized over the years that for the recuperation to work appropriately and the patients to get a good long-term solution to their needs, changes have to be made in the overall OVD structure (Guertin and Prostho, 2003).

4.2.1 Definition:

The OVD is normally described as the space between the two points that exist when the occlusal surfaces come in contact with each other. Hence, it is important to note that the OVD is a phenomenon that appears with the overall positioning of the teeth.

Hence, it is important to note here that the decision to change or alter the OVD at any stage cannot be a hasty or careless decision. This is so because any level of change, minor or major will require an appropriate recuperation plan for one arc, and at times, even both (Guertin and Prostho, 2003).

4.2.2 Vertical dimension at rest:

One of the biggest questions that people ask is whether or not dental wear and tear can directly lead to the overall deficiency of OVD? There are two different ideologies that emerge as an answer to this question (Guertin and Prostho, 2003).

Niswonger came up with the first concept after making observations and analyses of his personal experiences with his patients. His analyses helped him assert that that it was nature's course to preserve a consistent level of distance in the constant inter-occlusal space of nearly 3mm throughout an individual's life span. The methodology used to sustain this distance over the years is through the extrusion of the dento-alveolar composite which can help balance any natural or man-ensued dental wear that occurs. However, over the years, the advocates of this particular theory have concluded that the dental, muscular and articular spheres can possibly face sever damages with the alterations made in the VD of an individual (Guertin and Prostho, 2003).

The other ideology that was brought forth in response to the query of whether OVD was a direct result of dental wear has been supported by numerous cephalometric researches that have been conducted over the years. This ideology focuses on the impact of various scopes of facial structures, movements and expressions. The main idea that this particular phenomenon promotes is that the OVD undergoes changes at times after the dental wear process is finished or after the posterior teeth have been lost. The followers and advocates of this particular concept assert that the individual's natural neuromuscular structure is strong enough to adapt to the alterations that happen in the dento-alveolar construct (Guertin and Prostho, 2003).

However, it is important to note here that the deficiency or decrease of the OVD levels is nearly impossible to determine if the original location of the steady bony points of reference is not known i.e. before any dental alterations have taken place. This raises the important question of how, then, can an appropriate diagnosis be made? This is why dental history records play an important role. Furthermore, the methods mentioned in the prior paragraphs are all extremely helpful in allowing dentists to make an appropriate diagnosis. All of the methods mentioned here are established methods; none of them are new or experimental. Even though, all of these methods single-handedly might not be very helpful to a dentist but combining them together can also help a dentist make an informed diagnosis (Guertin and Prostho, 2003).

4.2.3 Increasing Occlusal Vertical Dimension:

Facial proportions

The sculpturer Phidias explains that the shapes that are agreeable to the human eye are formed when two separate entities are joined together respecting the proportions that each entity has. These, he calls, the golden number and the principle under which these shapes are formed, he calls, the golden rule. Hence, if we were to consider the golden rule in the dynamics of dentistry, we must understand the scope of the facial proportions. Looking at figure 2, we can clearly see that the golden rule exhibits the association between the pupil-commissure of the lips and the commissure of the lip-chin measures 1.618:1. It is important to note here that the space between the chin and the inside edge of the nose is mostly equivalent to the space between the commissure of the lips and the pupil (Dawson, 2007). Figure 2:

4.3 Centric Relation:

4.3.1 Definition:

In the realm of dentistry, centric relation is the mandibular jaw location which holds the top of the condyle in place far more superior and anterior then anything else inside the mandibular fossa. According to the prosthodontic glossary, the centric relation can defined as an anterior and superior braced position that is placed along the articular eminence of the glenoid fossa, with the articular disc interposed between the condyle and eminence (Dawson, 2007). It is the relationship between the upper and lower jaws when the mandibular condyles are in their transverse horizontal axis, regardless of the teeth contact (Krishan 1957).

The use of centric relation is mostly in situations when the recuperations of edentulous patients is needed, specifically those patients who have either the implant-braced hybrid or fixed and detachable prostheses. This process is used mainly because the dentist aims to reproducibly connect the individual's mandible and maxilla. However, alternate methods have to be at times used because the individual might not always have the teeth to clearly ascertain his own vertical dimension of the occlusion. This is why the condyle has to be placed in the same position every time if the consistency of its placement nearest to the most superior and anterior location inside the fossa has to be maintained (Dawson, 2007).

4.3.2 Philosophy of centric relation:

Maxillomandibular relationship in centric relation is the most controversial point in dentistry (Silverman, 1956). Centric relation is the essential key and factor in the study of the occlusion stability, so the determination of occlusal problem and TMJ evaluation are highly dependent upon the position of the lower jaw in the centric relation (Krishan, 1957). The centric relation exists irrespective of the presence or absence of teeth because it is essentially the relationship between the upper and lower jaw (Davies and Gray, 2001).

Moreover, the basic uses of an accurate Centric Relation recording should be made to reduce time spent, and then all the intraoral adjustments can be made at delivery. Some of the applicable situations include (Davies and Gray, 2001):

a. MI that is not clearly defined due to restored dentition.

b. Changing VDO

c. Occlusal scheme - group function rather than mutual protection.

d. TMJ disorder patients with occlusal discrepancies, as part of the etiology of the TMD (Davies and Gray, 2001).

Furthermore, in the picture used of the skull on the previous instance (FIG 2), the TMJ has been shaded a lighter shade so that the overall anatomy becomes more obvious to see. When analyzing the centric relation, the condyle has to be placed as centered within the glenoid fossa as possible, closer to the highest part and the back of the fossa. This particular placement is known as the centric relation. If and when the TM Joints are more or less healthy then they usually display this placement when the teeth have a slight space between them and the overall muscles of the mastication are in a calmed state. Preferably, this particular centric relation should exist when the overall teeth placement is close, with minimal to no space in between, within the individual's centric occlusion (Dawson, 2007).

4.3.3 Systems for recording Centric Relation:

The first step needs to be taken when the individual's wax rims start hitting the anterior. This happens when there is an obvious distance between the occlusion rims distal to the canines; this usually permits a normal recording. The procedure in this case must be to get the individual close, but to make sure that the patient is not tensed but relaxed, and then blot in the midline on the wax, making sure that both of the rims on the occlusion are marked or blotted distinctly. This is followed by a similar marking process in the canines' area using a different set of lines. The next step is to clearly indicate with a set marker the maxillary rim in the place where the overjet has initiated begins. If the four lines marked all overlap, then that is most likely the centric position; this of course will vary from individual to individual. The dentist will then ascertain that nothing is hitting the bottom by taking both of the recording bases out and then arranging the wax grooves in his hands. Then he will make several marks on the maxillary rim, nearly an inch away from each other, from the distal to the canine section. To make sure that all the recording done is steady, the material used for it must be long mesio-distally (Winkler, 1988).

The recording processes are normally the most intricate and tricky in application during the entire denture construction. It is also important to not only get good recording material but also to make sure that the entire recording structure is setup appropriately and strongly, because a perfect recording session can be very easily spoilt if the recoding structure was setup in a casual manner (Winkler, 1988).

Another important aspect while performing a denture construction is the phrasing and words used by the dentist. If a dentist mentions that they are recording a bite, then the most likely reaction of the patient would be to go into protrusive mode, instead the dentists should use words like "close," get the patient in close and then put their fingers on the buccal flange of the mandibular recording base. At this point the lines should be checked, if they overlap then that is most likely the centric position (Winkler, 1988). It is important to note here that many methods are used to record the centric relation and it is easy to find the centric relation using any one of them (Turrell, 1972). Furthermore, the clinician experience and the patient cooperation are the most essential factors to produce an accurate centric relation record (Kantor and Silverman, 1972). The four techniques currently practiced popularly are discussed below:

4.3.4 Recording techniques:

This is the one of the most accurate methods in comparison to the other techniques available (Turrell, 1972). This technique explains the importance of the phenomenon of mandible guiding, which means that the dentist's fingers have to be at right angles with upward pressure, and the thumbs have to be on the chin with downward pressure. Then one must softly manipulate the mandible so that the condyles fit in their optimum superior position in the fossa. The dentist should be careful not to over-manipulate the patient and let the condyles settle in a more posterior position (Hobo, Shillingburg and Whitsett, 1976).

2.

Chin-point guidance: this is not recommended due to the posterior displacement and stress on the bilaminar zone (Turrell, 1972).

McKee stated that the most important criteria for CR is the complete release of the inferior lateral pterygoid muscle during jaw closure. If it is not released, the condylar position could be inferior.

3.

Chin point guidance with anterior jig: this technique describes the use of anterior jig to make the separation between anterior teeth in order to assist the placement of the condyles to fit in the optimum superior position.

4.

Swallowing or free closure: this technique is described by Shanahan. He explains that "swallowing saliva is the determinative factor for obtaining vertical dimension and centric relation." The lower jaw seat in the centric relation can be controlled and manipulated by swallowing saliva (Bansal, 2008). Freese and Scheman in their study asserted that the swallowing method can be used as "an accurate physiologic means of checking and even of recording centric relation" (Shanahan, 1955).

4.3.5 Deprogrammer:

The deprogramming process is also very important. The most popular tool for deprogramming amongst the dentists is the butterfly Deprogrammer. The reason for the popularity of the butterfly deprogrammer is that it is a very simple mechanism to use and can be structured within 20 minutes in the room besides the chair where the individual will lie during the process. Also, this particular mechanism is very useful to provide swift cures for the phenomena of heightened indicators of temporomandibular dysfunction and the headaches caused by tension or stress. It is also helpful in forming or concluding accurate diagnoses for TMD as well as in the construction of a structured lab practiced splint. Furthermore, the butterfly deprogramming mechanism gives a dentist the option to identify the centric mandibular association in a very relaxed environment where the condyles can be very easily positioned in the most superior place within their fossae without any forced or dangerous operation (Winkler, 1988).

What makes the butterfly different from other deprogramming mechanisms is that it does not envelop the overall maxillary occlusion which makes it easy for the dentist to collect an appropriate, accurate and calming recording session during the whole denture construction process (Winkler, 1988).

Other advantages of the butterfly deprogramming include:

Quick application

Swift results

Easily portable

Inexpensive

Results attained are accepted by not only the doctors but also the patients

Can tremendously assist in conducting practical as well as experimental diagnosis and operation of the phenomenon of TMD

The material used to make is not only light but a cured construct that is normally utilized in the construction of the provisional bridges

This material, light and cured, can be used very efficiently in combination with the hand held VLC structure

It can also be made up of different materials like the cold cure acrylic that can be directly put into the patients' mouth (Winkler, 1988).

The butterfly deprogrammer can complete three main objectives which are as follows:

1. It should be able to provide immediate or quick release for the really severe symptoms that the patients are experiencing. Furthermore, the overall intensity and pain disappears completely or is reduced to a minimal level within an hour or two. The use of the butterfly deprogramming nearly eliminates the use or utilization of other medical remedies like the intake of muscle relaxants or analgesics, etc.

2. The butterfly deprogrammer also is of great assistance to either refute or confirm concluded diagnoses for the TMD.

3. It also helps in understanding the necessity of operating for a repositioning of a jaw or other jaw treatments (Winkler, 1988).

However, it is important to note that there have been dentistry cases where the butterfly deprogramming hasn't been always successful in providing the patients with swift or appropriate relief from the pain. If this tends to happen, then the butterfly deprogramming mechanism loses its overall importance and necessity which makes its setup and construction useless irrespective of how quickly it can be done (Winkler, 1988).

4.3.6-Factors that affect Centric Relation records:

Mounting in the mandibular model

It is very important that all of the recording devices are strongly and appropriately fitted in their place and attention has to be paid to the placement of the maxillary recording base so that it does not press against the seat or visa versa because this will cause changes and alterations in the recording. Some of the other common mistakes that can be made during recording that can affect the centric relation recording are (Watt, 1986):

1. The mounting ring is loosely placed.

2. The mounting ring has a little bit of wax or plaster on or under it.

3. The incisal guide pin has not been properly placed and set.

4. The condyles have been marked incorrectly and are not within the centric.

5. There is consistent contact between the models in the posterior position which is causing the overall recording to change.

6. The plaster used dried too quickly decreasing the overall time needed for the articulator to properly close.

7. The recording can be very inconsistent and unsteady which can result in the overall association between the models to alter.

8. The lubrication done for the cast and notches is not as required or at the appropriate level.

9. The articulator has not closed and the bottom of the model touches and connects with the mounting ring.

10. The models that are being used have not been properly seated in the recording mechanisms; this usually happens when the wax used ahs been placed in a wrong or an inappropriate place (Watt, 1986).

4.4-Anterior guidance:

The phenomenon of condylar guidance is very important in dentistry and has been very well researched over the years. However, the aspect of incisal guidance also has an equal part to play in the overall impact that it has on the mandible movements, positioning of the teeth as well as the OVD functions Boudrais (2005) in his study elaborates that "the importance of condylar guidance is well-known as well documented in the literature. Nevertheless, incisal guidance plays as important a role as the temporo-mandibular articulation in establishing a functional and harmonious occlusion, as much on the anterior teeth as the posterior teeth. The muscles of mastication and the temporomandibular articulation control mandibular movements when the teeth are not in contact. When the teeth are in contact, they guide the movements of the mandible with the exception of certain cases when there are limitations with the temporo-mandibular articulation."

However, it is important to note here that the overall impact that the condylar guidance has on the anterior movements and guidance is very minimal. However, the condyles' movement can be negatively influenced if the anterior design is weak or inappropriate. Boudrais (2005) further explains that "The direction of condylar movements has little influence on anterior guidance. A poor anterior guidance combined with balancing contacts on steep cuspal inclinations may lead to undesirable movements of the condyles. Nevertheless, there exists a certain degree of resilience during functional movements of the condyles. This adaptation mechanism is absent for anterior guidance since it depends on contacts between hard surfaces of the anterior teeth (Boudrais, 2005)."

Another aspect that anterior guidance can influence is the overall mandibular movements and the eventual necessity of the dental construction or reconstruction procedures. Again Boudrais (2005) explains that "Anterior guidance influences the direction of mandibular movements and permits the separation of the posterior teeth during these movements. It is influenced by the amount of overjet and overbite. When there is loss of anterior guidance, all the functional forces are transmitted to the remaining posterior teeth. The stress placed on these teeth, especially during lateral movements, result in excessive forces and may affect dental and periodontal structures (occlusal trauma, fracture)."

Boudrais (2005), in his study further explains the anterior design and teeth in comparison to the other teeth structures. He writes "the anterior teeth, especially the canines, possess a favourable bony support and reduce the forces transmitted to the posterior teeth during lateral functional movements. Often, the central incisors support protrusive contacts and contribute to the disengagement of the posterior teeth. When the posterior teeth must be restored, anterior guidance influences the morphological pattern as well as the height of the cuspal inclinations created by the dental technician. The weaker the degree of anterior guidance (open bite, minimal overbite), the less the occlusal surfaces of the posterior teeth should be accentuated."

He further adds that the overall anterior guidance that is either collected or altered by the dentist must be in at least one of the following situations:

1. "We restore several teeth in the anterior sextant,

2. We restore a canine that supports the occlusion in lateral excursions,

3. The vertical dimension is modified such as in the case of complete rehabilitation."

5-Ideal interocclusal record in the prosthesis:

Savabi and Nejatidanesh (2004) in their research note, "The accurate transfer of the position of implants to the definitive cast involves clinical and laboratory techniques. However, making a correct interocclusal record may be challenging in certain clinical situations. The correct maxillomandibular relation is critical for proper design of prosthesis and for providing an accurate occlusion. The interocclusal record is usually made after placement of the appropriate cover screws such that the recording medium can not fit properly on top of the implant or edentulous ridge and in many situations record bases may be required (Savabi and Nejatidanesh, 2004)."

5.1-Articulator Selection

Accurate prosthodontic processes allow not only the dentist but also the technician to generate restorations that are consistent with the physiology as well as the anatomy of the patient. This of course is reliant upon the use of dental apparatus that is precise, accurate and dependable. One of the most important instruments is the articulator. To fabricate the successful fixed or removable prosthodontic with exact the patient mandible movement and condylar inclination to prevent the occlusal interference and avoid massive adjustment in the patient mouth the type of articulator selection very important. According to the glossary of prosthodontics (1968), the articulator is "a mechanical instrument that represents the temporomandibular joints and jaws, to which maxillary and mandibular casts may be attached to simulate some or all mandibular movements." Similarly, Owen writes, "The contact relationship between the occlusal surfaces of the teeth during function."

5.1.1 Types of the Articulators:

There are three different types of articulators depending upon the hinge axis movement:

1-Fully Adjustable:

This articulator uses the "three dimentional movement of recorded mandibular movement." It allows the cast to simulate the temorpromandibular joint and mandibular movement (17). It is preferred that professional dentists and technician use this as they have more experience and skills of transferring the upper cast by facebow to the articulator without making any significant changes elsewhere (Victor, 1964).

2-Semi adjustable:

It is an instrument that duplicates the average lower jaw movement in centric relation (Dawson, 1974). It is very simple to use and does not need expertise to mount the cast. Similarly, the facebow is not mandatory to transfer the record (Victor, 1964).

3-Non adjustable (hinge):

This articulator is small and simple to open as well as close. It is used for occlusal relationship and not for any movement. It ought to be mentioned here that this articulator is not precise, and sometimes, dentists needs to adjust the prosthesis in the clinic (Victor, 1964).

5.2 -- Jaw record in fixed prosthodontic:

Materials for Jaw record in fixed prosthodontic include the following:

1. Digital display box:

2. Lower recording plate along with 5 temporary crowns as well as an electrical lead.

3. Upper recording plate along with 3 scribing points, as well as, central electronic contact point along with 4 temporary crowns, as well as, electrical lead attached.

Maxillomandibular relationship is one of the important points to fabricate fixed crown or bridge with accurate occlusal contact (Warren and Capp, 2001). This is particularly true when most of the posterior teeth are absent, which allows the dentist to look for the centric relation in order to transfer the accurate bite registration to articulator (Miller, 1989). Before the dentist starts the treatment he should take the accurate impression to produce the diagnostic casts for evaluation and analysis of (1) the teeth contact, as well as, (2) mandible functional movement. Furthermore, these accurate impressions are also useful for the treatment plan. And another advantage of the diagnostic cast is that it makes the diagnostic wax up and then it fabricates provisional restoration to maintain the same occlusion after the teeth is prepared (Rosenstiel and Land, 2001). Bite jaw relation should be taken to mounting the casts on the semi-adjustable articulator in the centric relation (Gerald, 1984). The Tempromandibular joint status and the muscles stability and health are very important to record interocclusal relationship, otherwise dentist will have to use the deprogramming occlusal splint to eliminate the muscles dysfunction and any occlusal interferences prior to any occlusal touch (Capp and Clayton, 1985). After the muscles and occlusal interferences are corrected, the accurate interocclusal record materials and techniques used to record the bite would allow the restoration insertion either without or with minimum occlusal adjustment. The materials used should be precise so that no dimensional change occurs and that they become hard after the setting (Christensen, 1983). There are some other techniques mentioned to produce the interocclusal record in Centric Relation. For instance, one author recommended the use of the last tooth as centric stop to avoid any changes in the vertical dimension (Ghazal, Albashaireh and Kern, 2008).

5.3 -- jaw relation for complete denture:

One of the most difficult procedures in the complete dentures is how the dentist obtains the correct position of the condyle (centric relation) and the occlusal vertical dimension during the interocclusal record (Dawson, 1985). The techniques and the materials used when starting the bite registration up to the insertion of the denture are very sensitive and important. The communication and cooperation between dentist and the dental lab technician is also very essential to complete the case with minimum mistakes and result that are acceptable. With regards to an edentulous patient, the first important procedure that should be done is to determine of centric relation record. This is because some of the complete dentures are not accepted here as the stability and function of occlusion is not maintained and the centric occlusion is not in harmony with centric relation (Rosenstiel and Land, 2001).

Both the maxillary, as well as, mandibular casts should be precisely connected to an articulator by utilizing maxillary record base, which should be retentive. A non-retentive maxillary record base more often than not outcomes from failure to adjust the resin (predominantly from the posterior border as well as palate) al through polymerization. On the other hand, laxity might take place by either over or under extension, or by utilizing of a lot of blockout. In instances where minimal looseness occurs, denture glue might be utilized to ensure that the record base is in position. If distinct looseness continues to exist, the dentist can save his time by recreating the record base before the jaw relation is recorded (Loney, 2009).

The dentist should make the rims somewhat higher than what is actually required (23 mm standard height which begins from the extension of the record base and ends at the rim). With this technique the dentist can reduce the height as needed (Loney, 2009).

The materials selection to fabricate the base plate wax rim is very essential. The soft and compressed material will produce inaccurate maxillomandibular relationship when patient is biting. During the bite registration the hard and dimensionally stable materials should be used to transfer the relation record to the lab to mount on the articulator without any change or damage (Loney, 2009).

During the wax rim in the patient's mouth, some relation should be recorded, which includes the arbitrary adjustment of Occlusion Rims for both maxillary and mandibular thereby establishing the Occlusal Vertical Dimension. Wax occlusal rim should be adjusted up to get not only an accurate occlusal vertical dimension but also make the TMJ stable and comfortable (Loney, 2009).

5.3.1-Hinge Axis Location

The human face can be viewed in three different planes: the first being frontal; the second being sagittal; and the third being horizontal. In each of these three planes the rotation of a mandible is taking place at a particular axis. This axis has two properties; it can either be stationary or it can be moving. When the mandible shifts sideway movement takes place in the horizontal plane. Also, during this sideways movement, if the orbiting plane drops down, the mandible is said to rotate in the sagittal axis. Here in the sagittal axis as the mandible moves and rotates, it does so around the Transverse Horizontal Axis. Transverse Horizontal Axis is a pretended line wherein the mandible moves. This rotation takes place during centric relation and is referred to as a hinge axis rotation.

5.3.2 Making a Facebow/Earbow Transfer

Facebow records of your patient are one of the most important diagnostic records because they help in achieving the calculated results by providing crucial information for your laboratory. Thus, articulator and facebow are primarily used in today's esthetic dentistry. The relationship of the maxillary dentition to the horizontal reference plane is conceived by facebow transfer and eventually it helps in acquiring the correct anatomical position when the maxillary cast is mounted on the articulator. Basically facebow transfer facilitates in constituing relationship between the upper teeth and the patient's head (Shannon, 2006).

Denar® Slidematic facebow furnishes the use of multiple transfer jigs with only one measuring bow. Without facebow transfer capability in the dental office, the mounting of maxillary cast can be handed over to the laboratory in some cases, and it implicates no loss of accuracy and no period of time (Shannon, 2006).

Bitefork assembly from the dental office is used to set up the maxillary cast by the laboratory as their Denar articulator can be attached with articulator index. On any Denar articulator the bitefork assembly is positioned by each articulator index in such a way that the relationship with the condyles is reproduced perfectly on the articulator. Facebow transfer is very simple as depicted by the illustrations inside. Denar slidematic facebow due to its easy handling is mostly used by dental assistant for taking this vital records (Shannon, 2006).

For accurate facebow records following materials are required:

1. Earbow

2. Bitefork and Transfer Jig Assembly

3. Reference plane locator

4. Reference Plane Maker

5. A rigid or reinforced cotton roll

6. Rigid bite registration material or baseplate wax

Tech Steps:

On the right side of the patient mark the anterior reference point with the help of the Reference Plane Locator and Marker. (Note: On an edentulous patient, the lower border of the upper lip should be considered for measuring (Shannon, 2006).) (Figure 3):

Establish three contact points for placing bite registration (Shannon, 2006). (Figure 4):

While placing the fork into the patient's mouth make sure that the bitefork arm is to the right of the patient and allineate the index notch with the patient's midline, so that it is parallel with his coronal and horizontal planes. To sustain the bite, place a rigid or reinforced cotton roll under the bitefork (Shannon, 2006).

On the patient's right connect the vertical shaft with clamp marked #2 and tighten very securely the finger screw on the earbow. Contraction is done to fix the vertical shaft to the measuring bow and avoid any kind of movement (Shannon, 2006). (Figure 5):

Untie the center wheel only after you have loosened the finger screws on clamp #1 and #2. The earbow will open to adjust to the patient's face. Slide the bitefork arm through clamp marked #2 to assemble the facebow on the patient. When the measuring bow's earpieces fit tightly into the patient's ear, tighten the centre wheel on the bow (Shannon, 2006). (Figure 6):

Align the pointer accurately with the anterior reference point by raising or lowering the bow and tighten clamps #1 and #2. While tightening the clamps make sure that bow is in place (Shannon, 2006). (Figure 7):

Let the patient rise and feel for himself that whether the bow is parallel to the horizon or not (Shannon, 2006). (Figure 8):

For removing the facebow from the patient, loosen the finger screws on the measuring bow and slide open the bow. Making sure that clamp #1 and #2 stays in tact remove the measuring bow from the transfer jig by loosening the finger screw (Shannon, 2006).

Tag the bitefork and transfer jig with the patient's name and place them in the storage medium till they are sent to the laboratory. As for the earbow and additional bitefork assembly, they are ready to be used on the next patient (Shannon, 2006).

All in all, it's the easiest and most reliable method that eliminates the chances of a remake. The anomalies in the results generated by the information provided to the laboratory are greatly reduced (Shannon, 2006).

5.3.3 Centric Position

The most common technique for the production of dentures is as follows. Plaster models of the upper jaw and lower jaw are prepared from the imprints, taken by the dentist, of the teeth of upper jaw and lower jaw of the patient. These models are simulated as human teeth in the articulator with the help of two parts connected with each other by two joints which plays the role of human jaw joints. Once the plaster models are placed the joints are adjusted according to the patient (Lang, 2009).

Most common method for establishing the centric position is the one in which the patient is asked to bite a plate like plastically deformable register. Imprints of upper jaw and lower jaw are thus obtained on the register. These imprints are tried to be seated with the plaster models of the upper and lower jaws. For this purpose the articulate joints representing the jaw joints are adjusted until and unless the plaster models, mounted on the articulate, fits into the imprints on the two sides of the register (Lang, 2009).

Second most common method consists of a plate fastened in the patient's mouth, by means of a plastically deformable mass to the upper and the lower jaw. These plates extend through the oral cavity. A supporting pin in the middle of the plate fastened to the lower jaw produces imprint on the wax layer attached on the bottomside of the plate attached to the upper jaw, upon infringement. After removing these plates from the patient's mouth, they are mounted on the plaster models in the articulator. The articulator joints are so adjusted as to make the pin dip exactly in the already existing imprint in the wax layer of upper jaw. Having done so, the centric position of the patient's jaws is achieved in the articulator (Lang, 2009).

Another commonly used method for establishing the centric position is a manipulation of the method just discussed. In this technique instead of simply impinging the needle into the wax layer the patient is asked to move his lower jaw to and fro and sideways. Thus a T-like shape is obtained on the wax layer attached to the lower side of the upper plate. A Gothic arch appears on the upper T-limb which is basically an upwardly arch. The point where the two T-limbs cross each other is taken as the centric position and serves as the reference point for attaining centric position in the articulator (Lang, 2009).

5.3.4 Reasons for using CR in edentulous patients

For an edentulous patient reclamation of first the oral function and second the facial form are the two main objectives served by the prosthodontic and surgical rehabilitation. The priority of these factors depends on the patient. A thorough understanding of the effects caused by dynamic jaw atrophy on the bones of jaws and as well as on the overlying soft tissues is very essential for planning a cogent treatment for bone augmentation of edentulous patients (Sonis, Fazio and Fang, 1995).