Jaw relation records for ﬁxed prosthodontics
Jaw relation records are a fundamental and crucial component of pro¬viding accurate, high-quality ﬁxed restorations. A disciplined and eﬃcient practitioner understands that the use of accurate records minimizes the need for intraoral adjustments before prosthesis delivery and can there¬fore reduce overall treatment time and cost. Because all dental materials have their inherent limitations and because there exists variability in intra¬oral conditions, learning to minimize discrepancies in making jaw relation records is critical.
This article reviews the concepts of jaw relation records (or interocclusal records) and discusses the selection of interocclusal records for a variety of clinical situations. In addition, articulator choice, the purpose of a facebow, and materials for jaw relation records are discussed. Some ‘‘pearls’’ are oﬀered to help avoid common problem areas, including making impressions, pouring impressions, mounting casts, and making interocclusal records.
If the goal of restorative treatment is to maintain a patient’s pretreatment intercuspation and vertical dimension of occlusion (VDO), casts should be mounted in a manner that maintains the same tooth-to-tooth relationship that existed before treatment. This maximum intercuspal position (MIP) facilitates treatment and works with the patient’s existing occlusion. The vast majority of cases treated fall within this MIP category. The situation becomes more diﬃcult if a patient requires extensive treatment or if the VDO needs to be altered. In these circumstances, a reproducible maxillo¬mandibular position from which treatment is performed is essential and requires a centric relation record made at the terminal hinge axis. This article deals with situations where the patient’s MIP and VDO do not change as a result of treatment.
Function of the jaw relation record
Jaw relation records, or interocclusal records, have the following functions:
(1) They provide the stability or support that the casts of the remaining dentition lack, (2) they reduce chair time for the delivery of the restoration, (3) they reduce the likelihood of making restorations in hyperocclusion or with¬out occlusal contacts, and (4) they reduce the chance of perforation of re¬storations being inserted with excessive adjustment or having to adjust the opposing dentition inappropriately.
For opposing casts to relate well, there must be a tripod of vertical support and horizontal stability between the two casts. A minimum of three widely spaced tooth-to-tooth contacts should be present during mounting to ensure adequate stability. Casts that rock or wobble due to an insuﬃcient tripod require an interocclusal record to stabilize them before mounting. Full-arch working and opposing casts frequently have suﬃcient occluding natural teeth to accurately position the casts in a stable MIP occlusion, and horizontal stability is generally present when there is good intercuspation between teeth. However, in a patient with worn occlusal surfaces, although a solid vertical tripod may be obtained, the horizontal stability may be inadequate to accurately mount the casts. The goal of the interocclusal record is to provide the support or stability that the casts of the remaining dentition lack.
Interocclusal records used to mount casts in MIP can be separated into two categories: (1) records made when a tripod of vertical support is avail¬able from the remaining tooth-to-tooth contacts (an ‘‘existing tripod’’ inter¬occlusal record) and (2) records made when a tripod of vertical support is not available from the remaining tooth-to-tooth contacts (a ‘‘created tripod’’ interocclusal record) .
The existing tripod interocclusal record
When there is a tripod of widely spaced contacts and good intercuspation of the teeth, an interocclusal record is not needed. In this situation, hand articulation is the most accurate means of mounting a mandibular cast to a maxillary cast. Practitioners frequently waste time and materials making an interocclusal record when one is not needed. In addition, the use of an interocclusal record when hand articulation is suﬃcient creates a potential for error because the record can often prevent the casts from fully inter¬cuspating (Figs. 1 and 2). Therefore, full-arch impressions made for a mini¬mum number of teeth being restored usually need no interocclusal record due to the number of intact occlusal contacts.
In patients where vertical support is adequate but horizontal stability is lacking, an interocclusal record is needed to mount casts. Elastomeric materials such as polyvinylsiloxane are ideal for making interocclusal records where only horizontal stability is needed [2,3]. However, their accuracy can be compromised if they are not properly trimmed. These records should be carefully trimmed to remove all areas of the record that contact soft tissues and the axial surfaces of the teeth (Fig. 3). This is done to minimize the areas where the casts and the record touch, allowing the practitioner to visualize how the casts seat into the record and ensuring that the record provides only the horizontal support, with the contacting teeth providing the vertical support.
The created tripod interocclusal record
A tripod of opposing teeth is present but without occlusal contacts
A practitioner has to ‘‘create’’ a tripod of vertical support where one does not exist to mount opposing casts. A classic example of a created tripod interocclusal record is a fully dentate patient who has teeth #18 through #20 prepared for a ﬁxed partial denture. Although the teeth are well positioned around the dental arch, the tooth preparations prevent the existence of the third leg of the tripod. In this situation, the tripod has to be created so that the working and opposing casts can be mounted accurately. The materials best suited for this purpose are those that are soft at placement and then become rigid before their removal from the mouth, such as waxes, resins, zinc oxide and eugenol pastes, and impression plasters. The materials of choice for the general practitioner are resins (DuraLay [Reliance Dental, Worth, Illinois] or GC Pattern Resin [GC America, Alsip, Illinois]) or waxes. Resin placed conservatively between the tooth preparations and the opposing teeth creates the needed leg of the tripod for mounting (Fig. 4). The practitioner should avoid the elastomeric materials for this situation because these materials exhibit compressibility and rebound, often resultingin an inaccurate mounting that may lead to the need for excessive adjust¬ments upon delivery of the restoration or the possibility of no occlusion between the restoration and the opposing teeth.
Opposing teeth are absent at one or more desired tripod stops
When teeth are absent at one or more potential tripod stops, a record base-occlusion rim is indicated to obtain support from the edentulous ridge. The practitioner may use a record base-occlusion rim made on a cast or can make an intraoral segmental interocclusal record composed of rigid setting materials that do not displace the soft tissues of the edentulous ridge at the time of placement. If the choice is a record base-occlusion rim, the record base must be made on the cast that is to be mounted and not on earlier made diagnostic casts . A record base made on one cast does not predictably transfer to another cast due to diﬀerences between the casts. These discrepancies are the result of minor diﬀerences in soft tissue dis¬placement and tooth position and diﬀerences from the dimensional accuracy of impression materials and dental stones.
The record base is adapted to the edentulous portion of the cast and often to the lingual surfaces of the remaining teeth to enhance stability and retention (Fig. 5). Record bases usually are made from light-activated resin or autopolymerizing resin. The occlusion rim is able to function only as a substitute for a leg of a tripod when the record base is stable in the mouth and on the cast. The occlusion rim can easily and cheaply be made from baseplate wax to imprint the cusp tips of the opposing teeth, or other mate¬rials may be used, including metal-impregnated wax or the more rigid of the elastomeric interocclusal recording materials (eg, Blu-Mousse; Parkell, Farmingdale, New York).
If the working cast with crown preparations contains the edentulous areas where tripod stops are desired, the record base cannot be made until the ﬁnal impression is made, poured, and separated and the cast is trimmed. This usually requires that the patient make a separate brief appointment for a jaw relationship record before fabrication of the restorations. However, if the edentulous areas are located in the opposing arch, the practitioner who has planned ahead may have the record base-occlusion rim made on the opposing cast before the ﬁnal impression visit, allowing the interocclusal record to be made at the ﬁnal impression appointment.
Because of the popularity of the elastomeric materials for interocclusal records, they are often abused. One situation where this is the case is when there is an absence of a tripod of support and there is a need to create the tripod. Polyvinylsiloxane and polyether are ineﬀective materials when creating a tripod of support due to their inherent compressibility. Although the materials are easy to use for interocclusal records, their use during the mounting of the casts can be technique sensitive. It is diﬃcult to objectively determine the amount of force that should be exerted on the casts when mounting them with the interocclusal record. Too much force can cause compression of the elastic record, resulting in some part of the casts placed too closely together, and too little force can allow for inadequate seating of the cast into the record, resulting in casts that are too far apart. Therefore, despite the relative accuracy and dimensional stability of elastomeric materials and their ease of use and convenience, their use in these cir¬cumstances is likely to result in an inaccurate mounting and subsequent diﬃculty in delivering the ﬁnal restoration because of no occlusion or a resulting heavy occlusion.
因为弹性记录材料广为流行而被滥用。其中一个例子就是当鼎足缺失而需要做一个鼎足的时候。聚乙烯材料和聚醚材料 因为其可被压缩的特性而不适合用来恢复鼎足，尽管使用这些材料非常简单，但是用它们做咬合记录材料上合架是件技术型非常敏感的工作。到底要用多大的力量来在上合架的时候固定住记录材料非常难确定，力量太大会将记录材料压缩而导致颌间距离减小，力量太小又会 导致颌间距离加大。 尽管弹性记录材料相对比较精确，空间稳定性也好，使用也方便，但是把它用在该场合会导致上合架不精确而咬合导致最终修复体或是咬合过高，或是咬合过低。
The use of prosthesis frameworks
For a variety of clinical conditions, a ﬁxed metal framework or a metal framework for a removable partial denture can be used to support an interocclusal record. The beneﬁt of using a metal framework to support an interocclusal record is that the metal framework usually has more stability and retention than a record base-occlusion rim. For instance, when one is remounting casts after the metal try-in of ﬁxed restorations, the recording material may be added directly to the metal framework . The framework may carry an elastic material to make a segmental existing tripod record or a rigid material to contact the opposing teeth and make a created tripod record. When a practitioner requests a metal framework to be returned for try-in before porcelain application, not only should the metal be examined for ﬁt, but also the opportunity should be taken to verify the accuracy of the articulation of the working casts. The added time in verifying the articu¬lation could save considerable time at the insertion appointment.
When fabricating ﬁxed restorations in combination with a removable partial denture (RPD), jaw relation records are often diﬃcult due to the diﬃculty in achieving good stability of a record base and occlusion rim. The ﬁtted framework of the RPD can be used as a record base, and the occlusion rim can be formed directly into the meshwork areas [4,5] (Fig. 6). The framework adds retention and stability for an interocclusal record, thereby increasing its accuracy.
When fabricating ﬁxed and removable prostheses, the use of an ad¬justable articulator usually reduces the amount of intraoral adjustment needed. A more anatomically sized articulator, such as a programmed adjustable or a semiadjustable articulator, better reproduces the mandibular border movements compared with a simple hinge articulator. An articulator that is more true to human size allows the restoration to be adjusted by the technician to a greater degree and to a closer approximation of the patient’s intraoral situation. A full-size adjustable or semi-adjustable articulator is an excellent investment for the dentist who does a substantial amount of crown and bridge.
Purpose of a facebow
The purpose of a facebow transfer is to orient the maxillary cast to the transverse axis of the articulator. Its use is limited to adjustable and semi-adjustable articulators. Facebows are not necessary if there will be no change in the VDO. However, if any alteration of the VDO is planned, as in a full-mouth rehabilitation, a facebow (and a full-sized articulator) should be used. Another positive aspect of using a facebow is that it makes it easier to mount a maxillary cast to a full-sized articulator.
Avoiding errors and inaccuracies
Inaccuracies in jaw relations can be caused by a number of factors besides a poor interocclusal record. Errors can be introduced anywhere from im¬pressions to cast accuracy to problems with the articulation of the casts. These areas are often overlooked and are as important for overall accuracy as the interocclusal record.
All impression materials, all dental stones or plasters, and all inter¬occlusal materials have inherent inaccuracies: they shrink or expand. Learn¬ing how to minimize these inaccuracies improves the end product and results in a more successful outcome to the practitioner and to the patient.
Accuracy of dental casts and their subsequent successful articulation are essential when trying to maximize quality while minimizing treatment time with a patient. The following ‘‘pearls’’ elucidate common problem areas and discuss how to handle them.
Movement during setting of material
Movement of the impression tray during the setting time of the im¬pression material leads to inaccuracy. Minor movement while making an impression for study casts may not be too harmful in the overall scheme of treatment; however, the same movement for a ﬁnal impression is detrimental to the fabrication of a ﬁxed restoration. Once the tray with impression material is seated in the mouth, it is essential that any movement by the operator or the patient be prevented. An impression tray should never be left in a patient’s mouth without being stabilized by the practitioner or dental assistant. Additionally, a patient should not be allowed to close into a full-arch impression tray at any time; the practitioner’s or dental assistant’s ﬁngers should prevent this from occurring.
Impression material dislodged from the impression tray
Dislodged impression material occurs most frequently with alginate impression material. If a plastic stock tray is used and if the impression tray is not adequately painted with adhesive, the alginate has to rely solely on the perforations in the tray and may separate from the tray as the impression is removed from the mouth. This may happen with a metal stock tray as well because adhesive is generally not used in these trays for added security. Once distorted, the alginate cannot be pushed back into place; a new impression has to be made. This separation of alginate from the impression tray may be overlooked as a non-essential factor or may go unnoticed. Separation of the impression material from the tray is a common cause of inaccurate casts.
Although less likely than with alginate, the same separation of impression material from an impression tray may occur with elastomeric ﬁnal impres¬sion materials. After removing any impression from a patient’s mouth, the overall adherence of the impression material to the tray should be examined. This step reduces cast inaccuracies and the resultant errors in the fabrication of a restoration.
Laying alginate on tabletop with long extensions
Alginate impression material that is unsupported by an impression tray is under stress. Using an impression tray that does not adequately match a patient’s arch size runs the risk that a large portion of the alginate will be unsupported and therefore may become distorted. In addition, after an alginate impression is made, the practitioner usually places it on a countertop with the overextended alginate in direct contact with the ﬂat surface. Any direct pressure on the unsupported alginate distorts the impression. Ideally, an impression as discussed would be made and then disinfected and poured in dental stone while being held in a holding ‘‘tree’’ so the impression tray hangs from its handle rather than rests on the countertop (Fig. 7).
Pouring casts on time
Certain impression materials, such as reversible and irreversible hydro-colloids (alginate), must be poured promptly after making an impression, or rapid distortion occurs. After disinfection of either impression material, a cast should be poured immediately. Failure to do so causes loss of water from the impression material. This loss of water distorts an impression and produces inaccuracies in the cast that aﬀect the working dies for a ﬁxed restoration or the articulation of the casts. It is important when using any impression material to read the manufacturer’s recommendations for the maximum time allowable before pouring the impression to reduce inaccuracies.
Casts have major blebs on occlusal surfaces aﬀecting articulation
The majority of dental casts have ‘‘blebs’’ on the occlusal surfaces of the teeth. If they are large enough and go unnoticed, the articulation of casts can be signiﬁcantly altered, leading to a false mounting of the casts. The occlusal surfaces of the teeth on the casts should be free of these blebs, which interfere with the proper relationship of the casts. After impressions are poured and before mounting the casts, the occlusal surfaces should be examined and freed of any major blebs that would interfere with an accurate intercuspation of the teeth.
Hand articulate whenever possible
In a fully dentate patient with good maximum intercuspation and a widely spaced tripod, the most accurate method of relating casts is by hand articulation. The use of an interocclusal record in such a situation can result in (1) the inability to accurately mount the casts due to the thickness of the recording materials (see Figs. 1 and 2), (2) wasted time, and (3) wasted material and, therefore, money.
Heels of the casts touch
Casts that are improperly trimmed may have interferences that make mounting diﬃcult. One common site for this is the heel of the casts. Casts that extend too far posteriorly behind the retromolar pad and the maxillary tuberosity often interfere when the casts are mounted. Sometimes this goes unnoticed, especially when these extensions are preceded by edentulous areas. Touching heels prevents interocclusal records from ﬁtting accurately to the casts and results in inaccurate mountings.
When a patient is asked to bite into a large amount of material, it is often impossible to determine whether their teeth are coming into contact with one another because the amount of material obscures the practitioner from visualizing good tooth contact (Figs. 8 and 9). In addition, when applying the material for this type of record, if part of it sets while the rest of it is dead soft, the accuracy is compromised. In general, interocclusal records should be made with a minimum of material between the teeth or applied to a record base.
Mouth open during triple tray impression
When a patient bites into a large amount of impression material, the teeth frequently do not make contact. Triple tray impressions are notorious for this because it is often diﬃcult to visualize tooth contact with the impression material in a patient’s mouth (Fig. 10). It may not be noticed until the dental laboratory pours the impression and mounts the casts that the patient had not closed completely. When using triple trays, it is essential that the practitioner runs the patient through the motion and discusses with them what it should feel like when they close down through the material. One should not assume that the patient would close all the way through the material without proper instruction. In addition, the teeth on the opposite side of the arch to be impressed should be examined, and contacts should be visualized between the teeth before making the impression. When the impression is seated in the mouth and the patient closes, the practitioner should re-examine these same tooth contacts to ensure that they are the same. If not, there is likelihood that the patient did not close correctly or fully through the impression material.
Casts moved during articulation
When mounting dental casts onto an articulator, it is essential that the maxillary and mandibular casts be joined in such a way as to avoid any potential movement. Even in patients with good intercuspation, if the casts are not held immobile during mounting, any slight movement translates into some amount of discrepancy. There are multiple methods of mounting casts. The best method is the use of a combination of rigid sticks and compound or sticky wax (Fig. 11). The casts must be dry when using these materials to avoid any movement. Sticky wax placed directly onto the opposing teeth can also be used; however, when the sticky wax is removed, the teeth often break oﬀ the cast or are severely broken.
 Freilich MA, Altieri JV, Wahle JJ. Principles for selecting interocclusal records for articulation of dentate and partially dentate casts. J Prosthet Dent 1992;68:361–7.
 Balthazar-Hart Y, Sandrik JL, Malone WFP, Mazur B, Hart T. Accuracy and dimensional stability of four interocclusal recording materials. J Prosthet Dent 1981;45:586–91.
 Fattore LD, Malone WFP, Sandrik JL, Mazur B, Hart T. Clincial evaluation of the accuracy of interocclusal recording materials. J Prosthet Dent 1984;51:152–7.
 McGivney GP, Castleberry DJ. McCracken’s removable partial denture prosthodontics. 8th ed. St. Louis: CV Mosby; 1989.
 Warren K, Capp N. A review of principles and techniques for making interocclusal records for mounting working casts. Int J Prosthodont 1990;3:341–8.