26
Australian Dental Journal, February, 1978 Volume 23, No. 1
The integration of technical services into dental restorative procedures Patrick J. Henry
ABSTRACT-A protocol for improved dentist-laboratory relations is presented. The mutual responsibilities and obligations of dentist and technician are outlined. Each step of the procedure is developed and projected at the level of case planning and diagnostic wax-up. Introduction
An increased demand for restorative dentistry has occurred in recent years. This is partly due to changing socio-economic trends and to an improved awareness and altered attitude by the public. Modern dental techniques, armamentarium and procedures have rendered the delivery of dental care considerably less unpleasant for the patient. The demand is likely to increase further in the future as the effects of improved public dental health and educational programmes become fully effective. Many restorative services require the utilization of dental laboratory services. However, over the years the dentist-technician relationship has been chronically plagued by various problems and frustrations. If the workload is to be met with satisfactory standards of treatment in light of the manpower problems that exist today, it will become increasingly necessary for the dentist-technician relationship to be one of mutual respect, co-ordination and bilateral understanding. The concept of the team and the realization that each member can contribute t o the whole, is the objective of modern dental thinkingl. The ability
1
King C. J., Richardson, J. T., and Cleveland, J. L., J&.-The technician as part of the prevention team. J.A.D.A., 92:2, 374-377 (Feb.) 1976.
to establish a responsibility of all team members can only improve its efficiency and ultimately, benefit the patient. The purpose of this paper is to review the problems that exist and suggest guidelines for the harmonious delivery of high standard restorative dental services. Emphasis will be placed largely on the fixed prosthodontic restorative service because it is in this area that most problems exist. Problems of the dentist-technician relationship
The common complaints of technicians relate to having received improper directions for the work being done, poor quality impressions, inadequate time scheduling, being treated as a lower form of human life and not having their bills paid promptly. Above all, the technician basically wants to be part of a team and is desirous of his fair share of prestige recognitionz. On the other hand, dentists, complain that prices are too high, work is of poor quality and is often not scheduled on time. As a result, barriers of mistrust and suspicion have been built up over the years. More recently, the improved training methods
2
Rothstein, R . J.-The dental health team. Philadelphia, J . B. Lippincott Co., 1970.
Australian Dental Journal, February, 1978
27
and educational programmes available for the modern dental technician have resulted in the development of a highly skilled and comparatively better educated technician, than formerly. The technological aspects of modern dentistry are pro-
I
a,-=.
I
Fi 1 .-Diagrammatic illustration depicting the bask grkciples of a work production situation. Production reakdown occurs when the chain of events between A and B become mismatched.
ceeding at a faster rate of development with respect to materials, i x t h ad s and innovations than what dental students L .I be comparatively taught in dental schools. C .ocomitantly, the emphasis on the laboratory aspccts nf indirect dental restorations has been decreaeril in the dental school curriculum. Whilst !!.e economic welfare of the laboratory indwtry i* dependent on the implementation of mor'xn trends, the graduating dentist is finding himself relatively limited with respect to his knowledge of laboratory procedures. Consequently, his ability to coordinate services at the technical level is today more compromised than ever. Applied social science An overview of the chain of events occurring in any generalized work production situation is seen in Fig. 1 . It is adapted to the prosthodontic situation by considering the dentist, A, to be responsible for the background research and development of the case project. The laboratory, B, is responsible for the actual technical production of the work. Between A and B is a continuum of task. Task differentiation and integration of task performance should follow a linear progression. It is co-ordinated and controlled by a sequential flow of decisions and functions. However, the system will break down when mismatch occurs. Mismatch involves an interruption in the sequential flow of task performance and occurs because A and B do not communicate regarding their mutual problems. Mismatch is prevented by further application of scientific strategy by A closer to the final objective and earlier involvement of B in the integration of task performance at the level of planning and development.
Fig. 2.-Diagrammatic illustration of the lnfegration of the laboratory as ects of fixed prosthodontics into the o v e n 1 patient treatment plan.
Application of these basic principles in the field of prosthodontics is as follows. Formulation of the treatment plan must involve liaison with the laboratory so that various tasks delegated to the technician can be co-ordinated and controlled. The laboratory requires precise directions as to what it is meant to achieve. These directions are provided by the dentist in the work authorization form, as illustrated by the blue-print of the provisional restoration study model, together with the diagnostic wax-up. Thus the relationships and mutual responsibilities of the dentist and laboratory are clearly delineated. Mismatch is avoided by the dentist checking key stages along the production line so that the final objective is realized according to the original treatment plan. To this end, the establishment of a definite protocol will be instrumental in preventing mismatch. Protocol objectives Employment of a definitive protocol imparts a discipline of organized thought and procedure to the delivery of restorative dental care. Many cases presenting for treatment are complex both clinically and technologically. Such cases require concrete liaison to co-ordinate the clinical and laboratory phases of treatment into an overall plan. Principles of protocol for the complex reconstructive case are directly applicable to the simpler, but no less critical, smaller three unit bridge case. The integration of laboratory considerations into the development of the treatment plan is illustrated in Fig. 2.
Australian Dental Journal, February, 1978
28 The provisional restoration must fulfill the cosmetic and functional expectations of both dentist and patient as far as tooth shape and position are concerned3. At this stage it is imperative that any required modification be made. The case cannot proceed to the laboratory until the provisional restoration is accepted in principle by the patient. It is less traumatic to all concerned to modify or remake a temporary restoration than what it is to remake a completed metal ceramic restoration. In this manner the determined, final esthetic form can be systematically controlled as a routine procedure4. Case planning is primarily achieved at the level of diagnostic casts mounted on the articulator in the dental office by the dentist. The resultant diagnostic wax-up is duplicated by an alginate impression, to cast a model on which clear plastic template shells" are thermoformed for use in fabrication of the temporary coverage. This clear template shell is used directly in the mouth over the teeth and soft tissues initially as a guide for gross correction of abnormal occlusal planes as determined at the diagnostic wax-up; as an aid in tooth preparation to monitor the amount of reduction; and as a carrying vehicle for temporary resin material in the fabrication of the temporary coverage. The thickness of the resultant temporary can then be measured to ensure adequate thickness of final restorative material whether it be metal for functional reasons or veneered ceramic for cosmetic reasons (Fig. 3). The final temporary coverage must then clinically meet the requirements of the provisional restoration. The colour may or may not be an influencing factor dependent on choice of material for the restoration. Where required in unusual circumstances, directly made plastic temporary restorations can be custom shaded at the chairside as tinted acrylic mixes are added intrinsically t o the template of the temporary coverages. Alternatively, already cured or processed temporaries can be modified extrinsically with external stains**. However, such techniques are not advised for routine use because they can create problems with subsequent patient acceptance of anterior ceramic
* Omnivac, Omnidental Corp., Harrisburg, PA, U.S.A. **Minute-Stains, George Tauh Products, Jersey City, N.J., U.S.A. Lustig. L. P., and Galabrun, J. M.-The provisional a blue print for the laboratory. Quin. restoration of Dent. Tech., 1: 35-43, 1976. 'Preston, J. D.-A systematic approach to the control of esthetic form. J. Prosth. D., 35:4, 393-402 (Apr.) 1976. ECleveland, J. L.. King, C. J., and Contino, S. M.Custom shading for temporary coverage restorations. J . Prosthet. D., 32:4, 425-427 (OCI.) 1974. 3
-
restorations and their inherent metameric limitations. In cases where the coronal shape of teeth is being simply changed for cosmetic or functional reasons, the provisional temporary restorations must still fulfill the patient's expectations. In such cases, a study cast of the temporary crowns is made and the template is constructed to be utilized by the technician as a further guide to coronal contour and form at the laboratory workbench, during wax-up and porcelain build-up procedures (Fig. 4). Thus, in either event a model of the provisional restoration becomes a blueprint for the laboratory construction of the final prosthesis as controlled by the specifications of the written work authorization (Fig. 3 and 4).
Laboratory work estimate The laboratory work estimate is an important factor in the development of the treatment plan. It can be given by the laboratory following diagnostic wax-up, which will have established precisely the extent and complexity of the final restoration. The dentist should forward duplicates of the diagnostic wax-up to the laboratory for cost estimation, or preferably present himself for personal negotiation. From such liaison, the laboratory will indicate the overall time required to complete the case and the likely number and distribution of stages that will require checking by the dentist. Such stages as try-in castings, ceramic biscuitbake, occlusal remount procedures and so forth will require co-ordination between clinical scheduling and laboratory fabrication. Finally, an actual cost estimate of economics involved can be included. The treatment plan appointment with the patient can then be total in concept and questions as to length and distribution of appointments can be answered precisely. A copy of the laboratory work estimate can be furnished to the office staff to enable them to plan appointment schedules in an organized and projected manner. Utilization of this system then makes the presentation of the financial aspect of the treatment plan flexible. An overall fee may be assessed to cover total treatment costs. Alternatively, fee structure can be presented as an estimation of professional fee plus a separate laboratory work cost estimate. Both approaches have advantages and disadvantages. The latter system is advantageous when commercial facilities are used because the responsibility for absorbing fluctuating prices of gold and other variables are removed from the dentist. For example, the potential hassle of the remake
Australian Dental Journal, February, 1978
Fig. 3.-a, Case for fixed bridge replacement of missing teeth. b Articulator mounted study casts a t terminal hinge position. c, Anterior view following elimination of occlhsal interference, establishment of proposed occlusal scheme and diagnostic wax-up. d. Occlusal view, diagnostic wax-up from which an alginate impression is made. e Plastic template vacuum formed over study cast of wax-up. f, Temporary bridge formed from resin filled iemplate. Measurement check for correct thickness. g. Insertion of temporary bridge. Protrusive check and verification of anterior guidance.
29
30
Australian Dental Journal, February, 1978
Fig. 4.-a, Case presenting for aesthetic modification of anterior teeth. b, Preparations completed and placement of individual temporary crowns. c. Study cast and template of provisional restorations. d, Occlusal view of template to be used as a guide for laboratory duplication of anterior guidance. e, Working cast of prepared teeth, not sectioned for dies. f, Template fitted to working caqt as a technician guide to establishing correct metal thickness and tooth form.
anterior ceramic bridge case, rejected by the patient because of borderline differences of esthetic opinion, can be more easily managed with the dentist not having to absorb remake costs. Similarly, many laboratories are accepting urgent cases under a step pricing formula. Simply stated, the faster the work is required the higher is the laboratory fee. Considerations of pre-paid dentistry may also influence choice of system for the particular case at hand. In either event, it is mandatory that all monies must be channelled through the dental office because it is unacceptable to involve third
party agencies or patients in direct dealings, financial or otherwise, with commercial dental laboratories. Responsibilities of the dentist Th e integration of the biologic and technical requirements of modern prosthodontics have been clearly outlineds. Whilst each member of the dental team has individual responsibilities, the coordinating leadership must come clearly from the dentist. “Zarb, G. A.. Gergman, B., Clayton, I. A., and Mackay, H. F. (Edits.)-Prosthetic treatment for partially edentulous patients. The C. V. Mosby Company. I n press.
31
Australian Dental Journal, February, 1978 The dentist is obligated to provide the technician with:I . An illustration of projected end result, as in diagnostic wax-up. 2. Good preparations, with eliminations of occlusal interference prior to preparation. 3. Adequate occlusal and facial clearance for appropriate restorative material. pre-checked by thickness gauge measurement of temporary coverage. 4. Full arch master casts mounted in an articulating instrument: Dies must be stable with margins clearly demarcated. Instructions for adjusting condylar and incisal guide controls. Specifications for occlusal anatomy and character of maximum intercuspation. Specifications for requirements of occlusal scheme in eccentric excursions. 5 . Instructions for personalized esthetics: i Specifications for shape and form (provisional restoration model). ii Shade and colour (buttons, guides). Occlusal considerations
In limited fixed prosthodontics, technicians can be delegated to carry out mounting procedures, where sufficient unprepared teeth remain to accurately index full arch master casts. Mounting can be verified when the dentist checks the wax-up. Nevertheless, centric occlusion is of such paramount importance that the dentist must assume total responsibility for final verification. Accordingly, it is preferable that all mounting procedures for extensive dentistry be carried out by the dentist. Hence the responsibility of the technician starts and ends on the articulator. Subsequent discrepancy evident only in the mouth cannot be ascribed to laboratory error. Laboratory time spent on waxing is directly proportional to the complexity of the case. Guichet's (1976) classification enables the dentist to specify the relative time and effort he desires the laboratory to expend to fabricate the prescribed occlusion7 (Fig. 5 ) . Consequently, the laboratory fee can be rationalized, resulting in better quality control, with improved communications and mellowed social relations between dentist and laboratorys. Aesthetic considerations
Shape and form of the laboratory fabrication is
7
Guichet, N. F.-Classification of occlural carvings. J . Prosthet. D., 35:l. 97-100 (Jan.) 1976. Guichet, N . F.-Specificetions for the occlusal aspects of dental restorations. J . Prosthet. D., 35:1, 101-102 (Jan.) 1976.
dictated by the study model of the provisional restoration. Mo>t problems arise from shade selection. The inexperienced dentist, untrained in colour perception, may elect to send the patient to the laboratory for shade selection. Such protocol is ill advised and experience is never gained by such CLASSIFICATION OF OCCLUSAL CARVINQS CLASS
DESCHlPTlON
ILLUSTRATION
LABOR
FACTOH
REFINED
I
MODIFIED WAX
I D 30% INCREASE
DROP WAX
50-1W?.INCRCASE
I1
AAA
CENTRIC CONTACTS (01
POINT CONTACT
I-'.)
TRIPOD CONTACTS
MINIMUM
SURCUARGF.
Fig. 5 .-Specifications for the relative amount of time and effort to be spent by the laboratory tn attain the prescribed occlusion. (From, Guichet, N. F.-Classification of occlusal carvings. J . Prosthet. Dent., 35:1, 97100 (Jan.) 1976).
evasion. Such avoidance of professional responsibility is instrumental in fostering poor laboratory relationships, with the dentist suffering a loss of professional prestige in the eyes of the patient. Technicians electively are better off not dealing with the public in this regard. The commercial laboratory does not have the environment, facility, atmosphere or economic structure for direct dealings with the patient. Every effort should be made to standardize the variables existing between dental office and commercial laboratory. Light source differences can be minimized by utilization of a standard light source such as the Ney-Litei-. Recently a further improvement has been introduced which attempts to record colour differentials on a digital scale, for comparative use in clinical and laboratory situationst. Despite the use of these systems, many problems remain to be solved, particularly the difficulties of metamerism as experienced with ceramo-metal restorations. Custom shade buttons are of some use in porcelain fused to metal situations, but are expensive to produce in large numbers, particularly for the variety of metals currently available.
;The J.M. Ney Co., Bloomfield, Conn., U.S.A. $Chromascan Shade Scanner, Sterndent Corp., Mt. Vernon. N.Y., U.S.A.
Australian Dental Journal, February, 1978
32 Difficulties arise when the commercially standardized shade guide does not match the natural tooth appearance and therefore cannot be sent to the laboratory to copy. The problem can be of greater significance in the limited anterior pro-
colours can be applied to the biscuit-bake or glazed try-in directly i n the mouth. Intended modifications can then be directly visualized by the dentist. The trial application can then be rinsed off, the restoration removed, and then restained in the laboratory or directly at the chairside. Thus many dentists are now completing their aesthetic modifications in the dental office, achieving a stained individualized characterization using inexpensive glazing furnaces. Alternatively, the restoration or shade guide can be modified directly in the mouth by stains. The guide is then dried, placed in a container and dispatched to the laboratory. The technician subsequently reestablishes the appearance by wetting the guide and this clinically determined appearance is used as his colour prescription when finalizing the restoration9.
Fig. 6.-Colour ring of pure porcelain colours obtainable from the laboratory porcelain powder kit. Modification of “body” colour buttons by coloured opaques to give a wider range. Profile view shows buttons reduced to approximate thickness of I mm porcelain.
The technician must fulfill the following obligations to the dentist:1. Precise adherence to the specifications of the work authorization. 2. Have respect for models and dies. 3. Know how t o work the articulator. 4. Have a basic knowledge of occlusal schemes at articulator level. 5. Know how to wax the extensive case. ( a ) how to get prescribed occlusion ( b ) how to get accurate margins (c) how to get accurate castings 6. In restorations veneered for esthetics: ( a ) to get optimal design for metal substructure ( b ) to satisfy esthetic requirements of the prescription ( c ) to have a n understanding of the biologic requirements of pontic form, embrasure space and axial contour. 7. Have a basic understanding of plaque control procedures in complicated restorations.
Responsibilities of the laboratory
cedure, as opposed to extensive full coverage restorations where more flexibility over total aesthetics exists. Most shade guides can be immediately improved by grinding off the heavily stained neck. When remaining natural teeth cannot be approximated to the shade guide, the colour ring of individual porcelain buttons is very useful. Individual body colours may be varied by trial firing of colour opaques on the under surface. Thus any shade button may be modified by several colour opaques o n the under surface to provide a greater range of flexibility. Similarly, the individual enamel colours may be interchanged to alternative body shades as compared to the pre-formed relationship that exists on the standardized shade guide (Fig. 6). Relative distribution of colour in a tooth can be captured photographically. Whilst photography is of n o value in duplicating colour in dental ceramics, it is helpful in accurately duplicating the relative distribution of enamel, precise location of hypoplastic spots, characteristics, interproximal staining, and translucencies within the incisal edge. Such a picture is worth a thousand words and can be used to supplement the drawn diagram on the work authorization form. Alternatively, the characterization map may be drawn directly on a study model. An improved kit of stains is available‘, whereby BVITA Chrom L. Stains. VITA ZAHNFABRIK, Sackingen, W. Germany.
Checking of processing through the laboratory
For the smlooth sequential flow of task integration to occur, a minimal number of laboratory stages have t o be checked by the dentist. The more time devoted to the earlier stages of fabrication, the less modification will be required a t the final try-in and insertion appointments. The following steps require verification:1. Wax-up:Check procedures carried out on the articulator, ( a ) occlusion
9
Dorney, L., Martin Halas Dental Co.-Personal munication.
com-
33
Australian Dental Journal, February, 1978
Fig. 1.-a, Laboratory check of interproximal space to allow pla ue control with interproximal brush*. b, Lingual embrasure form around pontic to permit easy entry of %rush. c, Interproximal space widened between splinted abutments to allow passage of “super floss”**. d, Check for space to allow passage of bridge floss-threader. (*John 0.Butler Co., Chicago, Ill., U.S.A. **Educational Health Prods., New Canaan, Conn., U.S.A.)
( b ) margins (c) contours ( d ) outline for prescribed esthetic veneer. 2. Castings:Subject to same articulator check list as for wax-up, together with, (e) clinical try-in using same check list ( f ) if it is advantageous for the technician to see the case clinically for any reason, arrangements should be made for him to attend this appointment. 3. Porcelain Biscuit-Bake:Subject to same check list as for castings, together with, (g) gingival contour adjustments ( h ) pontic form and adaptation (i) embrasure form to permit passage of floss or interdental brush as required for plaque control (Fig. 7 ) . (j) patient acceptance of form and shape. 4. Porcelain glaze and polish of axial contours:Subject to same check list as for biscuit-bake toget her with, ( k ) patient acceptance of colour and esthetics ( I ) possible finalization of customized characterization of colour and esthetics.
Method of checking laboratory stages The armamentarium required for checking the laboratory stages following return to the dental office is seen in Fig. 7. Presence or absence of contact on occhding surfaces is checked with shimstock*. Zins stearate powder is used to check precise location of contact on wax surfaces. Occlusal foil’?:: is used to check precise location of contact on metal or porcelain surfaces and is of the same order of thickness as shimstock. T h e resultant level of discrimination of the order of 12-15 microns, is required to reach the level of tactile sensibility of natural teeth. Hence i t should be employed at laboratory level. Defects readily visible to the naked eye are of the order of 30-50 microns or greater depending on visual acuity. Accordingly magnifying glasses, loops or low power stereoscopic microscopy are useful tools for checking the integrity and fit of cast restorations. *The Artus Corp. Englewood, N.J., U.S.A. **Hanel-Medinzinal, Nurtingen, W. Germany. Farmingdale, N.Y.,U.S.A.
Parkell,
34 Wax-up check procedure Clrecking tlcc, urticrrltitor - Complete seating of condyles and incisal pin in the centric position is checked with shimstock. On non-arcon instruments the condyles are locked in terminal hinge position to check maximum intercuspation. On arcon instruments, following application of the centric latch, seating of condyles against the condylar housing is checked with shimstock. Ready withdrawal of shim indicates lack of condylar contact and is indicative of built in occlusal interference causing condylar displacement. If shim can be withdrawn from underneath the set incisal pin, the vertical dimension is open by an amount greater in thickness than shimstock. Incisal tables which cannot conform to the desired anterior guidance throughout the entire range must be modified with coldcure acrylic t o prevent excessive abrasion of stone or wax, thereby preventing subsequent occlusal discrepancy. Checking seating of dies - All dies must be individually checked t o make sure they seat fully. Wax on pins or fine debris in the pin channel will prevent the die going completely to seat. Thus either the pattern in question will appear too high, or alternatively will appear occlusally correct but the final restoration in the mouth will be out of contact. Checking occlusal contacts - Location and size of contacts are checked with zinc stearate powder and amended as required using PKT waxing instruments (Fig. 8 ) . Functional movements are checked according to the occlusal scheme dictated by the treatment plan and entered on the work authorization form. Contact throughout the movement range will be indicated by burnishing of zinc stearate. Thus faulty placement of plane of occlusion and curve of Spee will result in eccentric interference, readily apparent by zinc stearate rubbings or lifting of the incisal pin from off the incisal guide table. Similarly cusp-height and ridge and groove direction are correlated with the zinc stearate marking pattern. Particular care should be put on the inspection of the lingual surfaces of maxillary anterior teeth to check equalization of contact throughout the entire range of anterior guidance. Final checking of centric stop pattern is crucial. Tripod patterns must demonstrate contact for cusp stabilization. Long centric wax-ups must be tested for equalization of contact at terminal hinge and throughout the desired centric range anteriorly. Immediate changes made in wax can be quick and easy and will result in only slight modification to the resultant castings. Time spent on refining of the wax-up is time well spent and will be returned
Australian Dental Journal, February, 1978 a hundredfold by the production of castings requiring little if any occlusal adjustment. Ctuting clrcch pro^ etlrrrr Castings should be returned from the laboratory in a sand bla\ted or air brushed state. without
Fig. 8.-Armamentarium required by dentist and technician for precise evaluation of check stages. a, Zinc stearate powder and brush. b PKT waxing instruments. c, Occlusal foil in diffdent colours for centric and movement contact patterns on castings. d, Occlusal registration strip (shimstock) and holder for determining presence or absence of contact on opposing surfaces.
visible evidence of grindings or burnishings. Internal surfaces can then be more readily examined under magnification for defects such as microsopic bubbles or imperfections. Many commercial laboratories routinely use stereoscopic microscope inspection of all castings prior to fitting. Castings are subject to the same check list as wax patterns. Occlusal contacts can be visible as direct contact burnishings of opposing surfaces, or by using occlusal foil, available in different colours to check centric and eccentric contacts. Interproximal contacts which appear satisfactory by holding them up to a light source may not hold shimstock, in which case they are classified as unsatisfactory. Utilization of dental floss alone in the mouth is not indicative of a satisfactory contact area. It may merely indicate that the space between the restoration is small enough to offer resistance to the passage of the floss. Occlusal high spots are removed using fine stones or small round finishing burs, and finished with fine mounted rubber points. Remount procedure Occlusal discrepancy requiring remount should be adjusted by the dentist and not returned to the laboratory for grind-in. Few technicians have the capability of carrying out precise occlusal adjustment for the extensive case following remount. Porcelain check procedure Whilst it is distinctly preferable from an occlusal point of view to avoid porcelain functional sur-
Australian Dental Journal, February, 1978
35
faces it is sometimes inevitable. For example lower anteriors requiring coronal restoration must be restored with porcelain incisal edges for esthetic reasons. Porcelain surfaces that contact in occlusion are subject to the same check procedures as
3. Act as a protective document for both dentist and laboratory in the event of litigation. Statutory requirements on dental laboratory operations vary widely geographically and it is mandatory that the dentist familiarize himself with
a
Fig. 9
-Work
Authorization Form.
for castings. Contacts are verified using different colour occlusal foil. The porcelain occluding surface has several inherent disadvantages related to the nature of the material. Firstly it must be fired and then ground-in to fit. Although high accuracy may be achieved, the comparative degree of precision available with the dropped wax gold casting procedure cannot be achieved with ceramic materials. Secondly, glazing the biscuit-bake involves further changes in vitrification which result in altered occlusal contact. This is most evident in attempts at tripodial porcelain configurations. Reglazing involves further slight change. Therefore, critical adjustments on glazed occluding surfaces should be polished, not reglazed. Impregnated rubber points can achieve a high polish, which is visually inseparable from glazed porcelain. The Written Work Authorization
The function of the work authorization is to:1. Clearly delineate responsibility. 2. Provide co-ordinating instructions f o r prescribed procedures.
the appropriate laws governing the practice of dentistry and conduct himself accordingly. Work authorization forms should be assemb!ed in tablet form so that carbon copies can be conveniently made for record purposes'*. Each stage in the laboratory production of fixed prosthodontic work is intrinsically important to the whole result. Whilst the success of the finished product reflects the degree of accuracy exercised during each step of the technic, it should not be confused or complicated by screeds OF writing at the earliest stage. An authorization should be simple. concise and clear cut to avoid confusion. In large cases it may be advantageous to issue ;I number of separate authorizations with each one covering the next stage of the reconstruction, or the original authorization can be amended as the case dictates. For example, considerations of difficult shade situations need not be made on the original authorization, but could be made at the
'I'
Henderson, D., and Frazier. Q.-Communicating with dental laboratory technicians. D. Clin. N. Amer., 14: 603-613, 1970.
36 time of returning the castings check stage to the laboratory. Written instructions can be complemented by additional data as the complexity of the case increases. Diagnostic wax-up, provisional model, specific shade buttons and photographic documentation can accompany the work authorization when indicated. Many laboratories encourage the use of tape recorder cassette auxiliary prescriptions to supplement the written authorization. A sample authorization form applicable to modern practice is seen in Fig. 9.
Choice of laboratory facility Three alternatives exist. The remotely situated commercial enterprise, the on-site facility as an integral part of the practice set-up and the commercial laboratory situated adjacent to the dental office. The latter system may be the compromise of choice for the general dentist with limited practice in simple prosthodontics. The on-site laboratory has the disadvantages of substantial financial outlay and additional overhead, with considerable time and financial investment in the training and long-term retention of the technician. Nevertheless, in such practices the logistic problems of transportation of armamentarium and models do not exist. Office liaison and treatment planning are simplified and standards are more readily maintained. The economic possibilities of prosthodontic practice are quite flexible and one dentist can support several technicians. Schedules
Australian Dental Journal, February, 1978 can be arranged to enable the dentist to attend meetings without the worry of the office coming to a standstill. Dentists exposed to such a system enjoy their practice life-style immensely and a genuine warm and lasting relationship can be developed with the technical staff. Conclusions
The degree of success of the finished product in restorative dentistry reflects the degree of accuracy exercised during each step of the procedure. Each step is intrinsically important to the end result and the importance of each step cannot be minimized. The mutual obligations and responsibilities of dentist and technician must be based on an understanding of the overall problems involved. The problems are programmed for satisfactory resolution at the level of diagnostic wax-up and treatment planning. It is incumbent upon the dentist subsequently to supply the technician with clear and precise directions. Acknowledgement
The author wishes to express his gratitude to Dr. J. A. Clayton, Professor of Crown and Bridge Prosthodontics, University of Michigan, for his inspiration and encouragement in the development of this protocol. 34 Outram Street, West Perth, W.A., 6005.
Australian Dental Journal, February, 1978 Volume 23, No. 1
The integration of technical services into dental restorative procedures Patrick J. Henry
ABSTRACT-A protocol for improved dentist-laboratory relations is presented. The mutual responsibilities and obligations of dentist and technician are outlined. Each step of the procedure is developed and projected at the level of case planning and diagnostic wax-up. Introduction
An increased demand for restorative dentistry has occurred in recent years. This is partly due to changing socio-economic trends and to an improved awareness and altered attitude by the public. Modern dental techniques, armamentarium and procedures have rendered the delivery of dental care considerably less unpleasant for the patient. The demand is likely to increase further in the future as the effects of improved public dental health and educational programmes become fully effective. Many restorative services require the utilization of dental laboratory services. However, over the years the dentist-technician relationship has been chronically plagued by various problems and frustrations. If the workload is to be met with satisfactory standards of treatment in light of the manpower problems that exist today, it will become increasingly necessary for the dentist-technician relationship to be one of mutual respect, co-ordination and bilateral understanding. The concept of the team and the realization that each member can contribute t o the whole, is the objective of modern dental thinkingl. The ability
1
King C. J., Richardson, J. T., and Cleveland, J. L., J&.-The technician as part of the prevention team. J.A.D.A., 92:2, 374-377 (Feb.) 1976.
to establish a responsibility of all team members can only improve its efficiency and ultimately, benefit the patient. The purpose of this paper is to review the problems that exist and suggest guidelines for the harmonious delivery of high standard restorative dental services. Emphasis will be placed largely on the fixed prosthodontic restorative service because it is in this area that most problems exist. Problems of the dentist-technician relationship
The common complaints of technicians relate to having received improper directions for the work being done, poor quality impressions, inadequate time scheduling, being treated as a lower form of human life and not having their bills paid promptly. Above all, the technician basically wants to be part of a team and is desirous of his fair share of prestige recognitionz. On the other hand, dentists, complain that prices are too high, work is of poor quality and is often not scheduled on time. As a result, barriers of mistrust and suspicion have been built up over the years. More recently, the improved training methods
2
Rothstein, R . J.-The dental health team. Philadelphia, J . B. Lippincott Co., 1970.
Australian Dental Journal, February, 1978
27
and educational programmes available for the modern dental technician have resulted in the development of a highly skilled and comparatively better educated technician, than formerly. The technological aspects of modern dentistry are pro-
I
a,-=.
I
Fi 1 .-Diagrammatic illustration depicting the bask grkciples of a work production situation. Production reakdown occurs when the chain of events between A and B become mismatched.
ceeding at a faster rate of development with respect to materials, i x t h ad s and innovations than what dental students L .I be comparatively taught in dental schools. C .ocomitantly, the emphasis on the laboratory aspccts nf indirect dental restorations has been decreaeril in the dental school curriculum. Whilst !!.e economic welfare of the laboratory indwtry i* dependent on the implementation of mor'xn trends, the graduating dentist is finding himself relatively limited with respect to his knowledge of laboratory procedures. Consequently, his ability to coordinate services at the technical level is today more compromised than ever. Applied social science An overview of the chain of events occurring in any generalized work production situation is seen in Fig. 1 . It is adapted to the prosthodontic situation by considering the dentist, A, to be responsible for the background research and development of the case project. The laboratory, B, is responsible for the actual technical production of the work. Between A and B is a continuum of task. Task differentiation and integration of task performance should follow a linear progression. It is co-ordinated and controlled by a sequential flow of decisions and functions. However, the system will break down when mismatch occurs. Mismatch involves an interruption in the sequential flow of task performance and occurs because A and B do not communicate regarding their mutual problems. Mismatch is prevented by further application of scientific strategy by A closer to the final objective and earlier involvement of B in the integration of task performance at the level of planning and development.
Fig. 2.-Diagrammatic illustration of the lnfegration of the laboratory as ects of fixed prosthodontics into the o v e n 1 patient treatment plan.
Application of these basic principles in the field of prosthodontics is as follows. Formulation of the treatment plan must involve liaison with the laboratory so that various tasks delegated to the technician can be co-ordinated and controlled. The laboratory requires precise directions as to what it is meant to achieve. These directions are provided by the dentist in the work authorization form, as illustrated by the blue-print of the provisional restoration study model, together with the diagnostic wax-up. Thus the relationships and mutual responsibilities of the dentist and laboratory are clearly delineated. Mismatch is avoided by the dentist checking key stages along the production line so that the final objective is realized according to the original treatment plan. To this end, the establishment of a definite protocol will be instrumental in preventing mismatch. Protocol objectives Employment of a definitive protocol imparts a discipline of organized thought and procedure to the delivery of restorative dental care. Many cases presenting for treatment are complex both clinically and technologically. Such cases require concrete liaison to co-ordinate the clinical and laboratory phases of treatment into an overall plan. Principles of protocol for the complex reconstructive case are directly applicable to the simpler, but no less critical, smaller three unit bridge case. The integration of laboratory considerations into the development of the treatment plan is illustrated in Fig. 2.
Australian Dental Journal, February, 1978
28 The provisional restoration must fulfill the cosmetic and functional expectations of both dentist and patient as far as tooth shape and position are concerned3. At this stage it is imperative that any required modification be made. The case cannot proceed to the laboratory until the provisional restoration is accepted in principle by the patient. It is less traumatic to all concerned to modify or remake a temporary restoration than what it is to remake a completed metal ceramic restoration. In this manner the determined, final esthetic form can be systematically controlled as a routine procedure4. Case planning is primarily achieved at the level of diagnostic casts mounted on the articulator in the dental office by the dentist. The resultant diagnostic wax-up is duplicated by an alginate impression, to cast a model on which clear plastic template shells" are thermoformed for use in fabrication of the temporary coverage. This clear template shell is used directly in the mouth over the teeth and soft tissues initially as a guide for gross correction of abnormal occlusal planes as determined at the diagnostic wax-up; as an aid in tooth preparation to monitor the amount of reduction; and as a carrying vehicle for temporary resin material in the fabrication of the temporary coverage. The thickness of the resultant temporary can then be measured to ensure adequate thickness of final restorative material whether it be metal for functional reasons or veneered ceramic for cosmetic reasons (Fig. 3). The final temporary coverage must then clinically meet the requirements of the provisional restoration. The colour may or may not be an influencing factor dependent on choice of material for the restoration. Where required in unusual circumstances, directly made plastic temporary restorations can be custom shaded at the chairside as tinted acrylic mixes are added intrinsically t o the template of the temporary coverages. Alternatively, already cured or processed temporaries can be modified extrinsically with external stains**. However, such techniques are not advised for routine use because they can create problems with subsequent patient acceptance of anterior ceramic
* Omnivac, Omnidental Corp., Harrisburg, PA, U.S.A. **Minute-Stains, George Tauh Products, Jersey City, N.J., U.S.A. Lustig. L. P., and Galabrun, J. M.-The provisional a blue print for the laboratory. Quin. restoration of Dent. Tech., 1: 35-43, 1976. 'Preston, J. D.-A systematic approach to the control of esthetic form. J. Prosth. D., 35:4, 393-402 (Apr.) 1976. ECleveland, J. L.. King, C. J., and Contino, S. M.Custom shading for temporary coverage restorations. J . Prosthet. D., 32:4, 425-427 (OCI.) 1974. 3
-
restorations and their inherent metameric limitations. In cases where the coronal shape of teeth is being simply changed for cosmetic or functional reasons, the provisional temporary restorations must still fulfill the patient's expectations. In such cases, a study cast of the temporary crowns is made and the template is constructed to be utilized by the technician as a further guide to coronal contour and form at the laboratory workbench, during wax-up and porcelain build-up procedures (Fig. 4). Thus, in either event a model of the provisional restoration becomes a blueprint for the laboratory construction of the final prosthesis as controlled by the specifications of the written work authorization (Fig. 3 and 4).
Laboratory work estimate The laboratory work estimate is an important factor in the development of the treatment plan. It can be given by the laboratory following diagnostic wax-up, which will have established precisely the extent and complexity of the final restoration. The dentist should forward duplicates of the diagnostic wax-up to the laboratory for cost estimation, or preferably present himself for personal negotiation. From such liaison, the laboratory will indicate the overall time required to complete the case and the likely number and distribution of stages that will require checking by the dentist. Such stages as try-in castings, ceramic biscuitbake, occlusal remount procedures and so forth will require co-ordination between clinical scheduling and laboratory fabrication. Finally, an actual cost estimate of economics involved can be included. The treatment plan appointment with the patient can then be total in concept and questions as to length and distribution of appointments can be answered precisely. A copy of the laboratory work estimate can be furnished to the office staff to enable them to plan appointment schedules in an organized and projected manner. Utilization of this system then makes the presentation of the financial aspect of the treatment plan flexible. An overall fee may be assessed to cover total treatment costs. Alternatively, fee structure can be presented as an estimation of professional fee plus a separate laboratory work cost estimate. Both approaches have advantages and disadvantages. The latter system is advantageous when commercial facilities are used because the responsibility for absorbing fluctuating prices of gold and other variables are removed from the dentist. For example, the potential hassle of the remake
Australian Dental Journal, February, 1978
Fig. 3.-a, Case for fixed bridge replacement of missing teeth. b Articulator mounted study casts a t terminal hinge position. c, Anterior view following elimination of occlhsal interference, establishment of proposed occlusal scheme and diagnostic wax-up. d. Occlusal view, diagnostic wax-up from which an alginate impression is made. e Plastic template vacuum formed over study cast of wax-up. f, Temporary bridge formed from resin filled iemplate. Measurement check for correct thickness. g. Insertion of temporary bridge. Protrusive check and verification of anterior guidance.
29
30
Australian Dental Journal, February, 1978
Fig. 4.-a, Case presenting for aesthetic modification of anterior teeth. b, Preparations completed and placement of individual temporary crowns. c. Study cast and template of provisional restorations. d, Occlusal view of template to be used as a guide for laboratory duplication of anterior guidance. e, Working cast of prepared teeth, not sectioned for dies. f, Template fitted to working caqt as a technician guide to establishing correct metal thickness and tooth form.
anterior ceramic bridge case, rejected by the patient because of borderline differences of esthetic opinion, can be more easily managed with the dentist not having to absorb remake costs. Similarly, many laboratories are accepting urgent cases under a step pricing formula. Simply stated, the faster the work is required the higher is the laboratory fee. Considerations of pre-paid dentistry may also influence choice of system for the particular case at hand. In either event, it is mandatory that all monies must be channelled through the dental office because it is unacceptable to involve third
party agencies or patients in direct dealings, financial or otherwise, with commercial dental laboratories. Responsibilities of the dentist Th e integration of the biologic and technical requirements of modern prosthodontics have been clearly outlineds. Whilst each member of the dental team has individual responsibilities, the coordinating leadership must come clearly from the dentist. “Zarb, G. A.. Gergman, B., Clayton, I. A., and Mackay, H. F. (Edits.)-Prosthetic treatment for partially edentulous patients. The C. V. Mosby Company. I n press.
31
Australian Dental Journal, February, 1978 The dentist is obligated to provide the technician with:I . An illustration of projected end result, as in diagnostic wax-up. 2. Good preparations, with eliminations of occlusal interference prior to preparation. 3. Adequate occlusal and facial clearance for appropriate restorative material. pre-checked by thickness gauge measurement of temporary coverage. 4. Full arch master casts mounted in an articulating instrument: Dies must be stable with margins clearly demarcated. Instructions for adjusting condylar and incisal guide controls. Specifications for occlusal anatomy and character of maximum intercuspation. Specifications for requirements of occlusal scheme in eccentric excursions. 5 . Instructions for personalized esthetics: i Specifications for shape and form (provisional restoration model). ii Shade and colour (buttons, guides). Occlusal considerations
In limited fixed prosthodontics, technicians can be delegated to carry out mounting procedures, where sufficient unprepared teeth remain to accurately index full arch master casts. Mounting can be verified when the dentist checks the wax-up. Nevertheless, centric occlusion is of such paramount importance that the dentist must assume total responsibility for final verification. Accordingly, it is preferable that all mounting procedures for extensive dentistry be carried out by the dentist. Hence the responsibility of the technician starts and ends on the articulator. Subsequent discrepancy evident only in the mouth cannot be ascribed to laboratory error. Laboratory time spent on waxing is directly proportional to the complexity of the case. Guichet's (1976) classification enables the dentist to specify the relative time and effort he desires the laboratory to expend to fabricate the prescribed occlusion7 (Fig. 5 ) . Consequently, the laboratory fee can be rationalized, resulting in better quality control, with improved communications and mellowed social relations between dentist and laboratorys. Aesthetic considerations
Shape and form of the laboratory fabrication is
7
Guichet, N. F.-Classification of occlural carvings. J . Prosthet. D., 35:l. 97-100 (Jan.) 1976. Guichet, N . F.-Specificetions for the occlusal aspects of dental restorations. J . Prosthet. D., 35:1, 101-102 (Jan.) 1976.
dictated by the study model of the provisional restoration. Mo>t problems arise from shade selection. The inexperienced dentist, untrained in colour perception, may elect to send the patient to the laboratory for shade selection. Such protocol is ill advised and experience is never gained by such CLASSIFICATION OF OCCLUSAL CARVINQS CLASS
DESCHlPTlON
ILLUSTRATION
LABOR
FACTOH
REFINED
I
MODIFIED WAX
I D 30% INCREASE
DROP WAX
50-1W?.INCRCASE
I1
AAA
CENTRIC CONTACTS (01
POINT CONTACT
I-'.)
TRIPOD CONTACTS
MINIMUM
SURCUARGF.
Fig. 5 .-Specifications for the relative amount of time and effort to be spent by the laboratory tn attain the prescribed occlusion. (From, Guichet, N. F.-Classification of occlusal carvings. J . Prosthet. Dent., 35:1, 97100 (Jan.) 1976).
evasion. Such avoidance of professional responsibility is instrumental in fostering poor laboratory relationships, with the dentist suffering a loss of professional prestige in the eyes of the patient. Technicians electively are better off not dealing with the public in this regard. The commercial laboratory does not have the environment, facility, atmosphere or economic structure for direct dealings with the patient. Every effort should be made to standardize the variables existing between dental office and commercial laboratory. Light source differences can be minimized by utilization of a standard light source such as the Ney-Litei-. Recently a further improvement has been introduced which attempts to record colour differentials on a digital scale, for comparative use in clinical and laboratory situationst. Despite the use of these systems, many problems remain to be solved, particularly the difficulties of metamerism as experienced with ceramo-metal restorations. Custom shade buttons are of some use in porcelain fused to metal situations, but are expensive to produce in large numbers, particularly for the variety of metals currently available.
;The J.M. Ney Co., Bloomfield, Conn., U.S.A. $Chromascan Shade Scanner, Sterndent Corp., Mt. Vernon. N.Y., U.S.A.
Australian Dental Journal, February, 1978
32 Difficulties arise when the commercially standardized shade guide does not match the natural tooth appearance and therefore cannot be sent to the laboratory to copy. The problem can be of greater significance in the limited anterior pro-
colours can be applied to the biscuit-bake or glazed try-in directly i n the mouth. Intended modifications can then be directly visualized by the dentist. The trial application can then be rinsed off, the restoration removed, and then restained in the laboratory or directly at the chairside. Thus many dentists are now completing their aesthetic modifications in the dental office, achieving a stained individualized characterization using inexpensive glazing furnaces. Alternatively, the restoration or shade guide can be modified directly in the mouth by stains. The guide is then dried, placed in a container and dispatched to the laboratory. The technician subsequently reestablishes the appearance by wetting the guide and this clinically determined appearance is used as his colour prescription when finalizing the restoration9.
Fig. 6.-Colour ring of pure porcelain colours obtainable from the laboratory porcelain powder kit. Modification of “body” colour buttons by coloured opaques to give a wider range. Profile view shows buttons reduced to approximate thickness of I mm porcelain.
The technician must fulfill the following obligations to the dentist:1. Precise adherence to the specifications of the work authorization. 2. Have respect for models and dies. 3. Know how t o work the articulator. 4. Have a basic knowledge of occlusal schemes at articulator level. 5. Know how to wax the extensive case. ( a ) how to get prescribed occlusion ( b ) how to get accurate margins (c) how to get accurate castings 6. In restorations veneered for esthetics: ( a ) to get optimal design for metal substructure ( b ) to satisfy esthetic requirements of the prescription ( c ) to have a n understanding of the biologic requirements of pontic form, embrasure space and axial contour. 7. Have a basic understanding of plaque control procedures in complicated restorations.
Responsibilities of the laboratory
cedure, as opposed to extensive full coverage restorations where more flexibility over total aesthetics exists. Most shade guides can be immediately improved by grinding off the heavily stained neck. When remaining natural teeth cannot be approximated to the shade guide, the colour ring of individual porcelain buttons is very useful. Individual body colours may be varied by trial firing of colour opaques on the under surface. Thus any shade button may be modified by several colour opaques o n the under surface to provide a greater range of flexibility. Similarly, the individual enamel colours may be interchanged to alternative body shades as compared to the pre-formed relationship that exists on the standardized shade guide (Fig. 6). Relative distribution of colour in a tooth can be captured photographically. Whilst photography is of n o value in duplicating colour in dental ceramics, it is helpful in accurately duplicating the relative distribution of enamel, precise location of hypoplastic spots, characteristics, interproximal staining, and translucencies within the incisal edge. Such a picture is worth a thousand words and can be used to supplement the drawn diagram on the work authorization form. Alternatively, the characterization map may be drawn directly on a study model. An improved kit of stains is available‘, whereby BVITA Chrom L. Stains. VITA ZAHNFABRIK, Sackingen, W. Germany.
Checking of processing through the laboratory
For the smlooth sequential flow of task integration to occur, a minimal number of laboratory stages have t o be checked by the dentist. The more time devoted to the earlier stages of fabrication, the less modification will be required a t the final try-in and insertion appointments. The following steps require verification:1. Wax-up:Check procedures carried out on the articulator, ( a ) occlusion
9
Dorney, L., Martin Halas Dental Co.-Personal munication.
com-
33
Australian Dental Journal, February, 1978
Fig. 1.-a, Laboratory check of interproximal space to allow pla ue control with interproximal brush*. b, Lingual embrasure form around pontic to permit easy entry of %rush. c, Interproximal space widened between splinted abutments to allow passage of “super floss”**. d, Check for space to allow passage of bridge floss-threader. (*John 0.Butler Co., Chicago, Ill., U.S.A. **Educational Health Prods., New Canaan, Conn., U.S.A.)
( b ) margins (c) contours ( d ) outline for prescribed esthetic veneer. 2. Castings:Subject to same articulator check list as for wax-up, together with, (e) clinical try-in using same check list ( f ) if it is advantageous for the technician to see the case clinically for any reason, arrangements should be made for him to attend this appointment. 3. Porcelain Biscuit-Bake:Subject to same check list as for castings, together with, (g) gingival contour adjustments ( h ) pontic form and adaptation (i) embrasure form to permit passage of floss or interdental brush as required for plaque control (Fig. 7 ) . (j) patient acceptance of form and shape. 4. Porcelain glaze and polish of axial contours:Subject to same check list as for biscuit-bake toget her with, ( k ) patient acceptance of colour and esthetics ( I ) possible finalization of customized characterization of colour and esthetics.
Method of checking laboratory stages The armamentarium required for checking the laboratory stages following return to the dental office is seen in Fig. 7. Presence or absence of contact on occhding surfaces is checked with shimstock*. Zins stearate powder is used to check precise location of contact on wax surfaces. Occlusal foil’?:: is used to check precise location of contact on metal or porcelain surfaces and is of the same order of thickness as shimstock. T h e resultant level of discrimination of the order of 12-15 microns, is required to reach the level of tactile sensibility of natural teeth. Hence i t should be employed at laboratory level. Defects readily visible to the naked eye are of the order of 30-50 microns or greater depending on visual acuity. Accordingly magnifying glasses, loops or low power stereoscopic microscopy are useful tools for checking the integrity and fit of cast restorations. *The Artus Corp. Englewood, N.J., U.S.A. **Hanel-Medinzinal, Nurtingen, W. Germany. Farmingdale, N.Y.,U.S.A.
Parkell,
34 Wax-up check procedure Clrecking tlcc, urticrrltitor - Complete seating of condyles and incisal pin in the centric position is checked with shimstock. On non-arcon instruments the condyles are locked in terminal hinge position to check maximum intercuspation. On arcon instruments, following application of the centric latch, seating of condyles against the condylar housing is checked with shimstock. Ready withdrawal of shim indicates lack of condylar contact and is indicative of built in occlusal interference causing condylar displacement. If shim can be withdrawn from underneath the set incisal pin, the vertical dimension is open by an amount greater in thickness than shimstock. Incisal tables which cannot conform to the desired anterior guidance throughout the entire range must be modified with coldcure acrylic t o prevent excessive abrasion of stone or wax, thereby preventing subsequent occlusal discrepancy. Checking seating of dies - All dies must be individually checked t o make sure they seat fully. Wax on pins or fine debris in the pin channel will prevent the die going completely to seat. Thus either the pattern in question will appear too high, or alternatively will appear occlusally correct but the final restoration in the mouth will be out of contact. Checking occlusal contacts - Location and size of contacts are checked with zinc stearate powder and amended as required using PKT waxing instruments (Fig. 8 ) . Functional movements are checked according to the occlusal scheme dictated by the treatment plan and entered on the work authorization form. Contact throughout the movement range will be indicated by burnishing of zinc stearate. Thus faulty placement of plane of occlusion and curve of Spee will result in eccentric interference, readily apparent by zinc stearate rubbings or lifting of the incisal pin from off the incisal guide table. Similarly cusp-height and ridge and groove direction are correlated with the zinc stearate marking pattern. Particular care should be put on the inspection of the lingual surfaces of maxillary anterior teeth to check equalization of contact throughout the entire range of anterior guidance. Final checking of centric stop pattern is crucial. Tripod patterns must demonstrate contact for cusp stabilization. Long centric wax-ups must be tested for equalization of contact at terminal hinge and throughout the desired centric range anteriorly. Immediate changes made in wax can be quick and easy and will result in only slight modification to the resultant castings. Time spent on refining of the wax-up is time well spent and will be returned
Australian Dental Journal, February, 1978 a hundredfold by the production of castings requiring little if any occlusal adjustment. Ctuting clrcch pro^ etlrrrr Castings should be returned from the laboratory in a sand bla\ted or air brushed state. without
Fig. 8.-Armamentarium required by dentist and technician for precise evaluation of check stages. a, Zinc stearate powder and brush. b PKT waxing instruments. c, Occlusal foil in diffdent colours for centric and movement contact patterns on castings. d, Occlusal registration strip (shimstock) and holder for determining presence or absence of contact on opposing surfaces.
visible evidence of grindings or burnishings. Internal surfaces can then be more readily examined under magnification for defects such as microsopic bubbles or imperfections. Many commercial laboratories routinely use stereoscopic microscope inspection of all castings prior to fitting. Castings are subject to the same check list as wax patterns. Occlusal contacts can be visible as direct contact burnishings of opposing surfaces, or by using occlusal foil, available in different colours to check centric and eccentric contacts. Interproximal contacts which appear satisfactory by holding them up to a light source may not hold shimstock, in which case they are classified as unsatisfactory. Utilization of dental floss alone in the mouth is not indicative of a satisfactory contact area. It may merely indicate that the space between the restoration is small enough to offer resistance to the passage of the floss. Occlusal high spots are removed using fine stones or small round finishing burs, and finished with fine mounted rubber points. Remount procedure Occlusal discrepancy requiring remount should be adjusted by the dentist and not returned to the laboratory for grind-in. Few technicians have the capability of carrying out precise occlusal adjustment for the extensive case following remount. Porcelain check procedure Whilst it is distinctly preferable from an occlusal point of view to avoid porcelain functional sur-
Australian Dental Journal, February, 1978
35
faces it is sometimes inevitable. For example lower anteriors requiring coronal restoration must be restored with porcelain incisal edges for esthetic reasons. Porcelain surfaces that contact in occlusion are subject to the same check procedures as
3. Act as a protective document for both dentist and laboratory in the event of litigation. Statutory requirements on dental laboratory operations vary widely geographically and it is mandatory that the dentist familiarize himself with
a
Fig. 9
-Work
Authorization Form.
for castings. Contacts are verified using different colour occlusal foil. The porcelain occluding surface has several inherent disadvantages related to the nature of the material. Firstly it must be fired and then ground-in to fit. Although high accuracy may be achieved, the comparative degree of precision available with the dropped wax gold casting procedure cannot be achieved with ceramic materials. Secondly, glazing the biscuit-bake involves further changes in vitrification which result in altered occlusal contact. This is most evident in attempts at tripodial porcelain configurations. Reglazing involves further slight change. Therefore, critical adjustments on glazed occluding surfaces should be polished, not reglazed. Impregnated rubber points can achieve a high polish, which is visually inseparable from glazed porcelain. The Written Work Authorization
The function of the work authorization is to:1. Clearly delineate responsibility. 2. Provide co-ordinating instructions f o r prescribed procedures.
the appropriate laws governing the practice of dentistry and conduct himself accordingly. Work authorization forms should be assemb!ed in tablet form so that carbon copies can be conveniently made for record purposes'*. Each stage in the laboratory production of fixed prosthodontic work is intrinsically important to the whole result. Whilst the success of the finished product reflects the degree of accuracy exercised during each step of the technic, it should not be confused or complicated by screeds OF writing at the earliest stage. An authorization should be simple. concise and clear cut to avoid confusion. In large cases it may be advantageous to issue ;I number of separate authorizations with each one covering the next stage of the reconstruction, or the original authorization can be amended as the case dictates. For example, considerations of difficult shade situations need not be made on the original authorization, but could be made at the
'I'
Henderson, D., and Frazier. Q.-Communicating with dental laboratory technicians. D. Clin. N. Amer., 14: 603-613, 1970.
36 time of returning the castings check stage to the laboratory. Written instructions can be complemented by additional data as the complexity of the case increases. Diagnostic wax-up, provisional model, specific shade buttons and photographic documentation can accompany the work authorization when indicated. Many laboratories encourage the use of tape recorder cassette auxiliary prescriptions to supplement the written authorization. A sample authorization form applicable to modern practice is seen in Fig. 9.
Choice of laboratory facility Three alternatives exist. The remotely situated commercial enterprise, the on-site facility as an integral part of the practice set-up and the commercial laboratory situated adjacent to the dental office. The latter system may be the compromise of choice for the general dentist with limited practice in simple prosthodontics. The on-site laboratory has the disadvantages of substantial financial outlay and additional overhead, with considerable time and financial investment in the training and long-term retention of the technician. Nevertheless, in such practices the logistic problems of transportation of armamentarium and models do not exist. Office liaison and treatment planning are simplified and standards are more readily maintained. The economic possibilities of prosthodontic practice are quite flexible and one dentist can support several technicians. Schedules
Australian Dental Journal, February, 1978 can be arranged to enable the dentist to attend meetings without the worry of the office coming to a standstill. Dentists exposed to such a system enjoy their practice life-style immensely and a genuine warm and lasting relationship can be developed with the technical staff. Conclusions
The degree of success of the finished product in restorative dentistry reflects the degree of accuracy exercised during each step of the procedure. Each step is intrinsically important to the end result and the importance of each step cannot be minimized. The mutual obligations and responsibilities of dentist and technician must be based on an understanding of the overall problems involved. The problems are programmed for satisfactory resolution at the level of diagnostic wax-up and treatment planning. It is incumbent upon the dentist subsequently to supply the technician with clear and precise directions. Acknowledgement
The author wishes to express his gratitude to Dr. J. A. Clayton, Professor of Crown and Bridge Prosthodontics, University of Michigan, for his inspiration and encouragement in the development of this protocol. 34 Outram Street, West Perth, W.A., 6005.
