Evaluating dentures
refractory
cast wax-ups
for removable
partial
Richard P. Frank, D.D.S., M.S.D.* University
of Washington,
School
of
Dentistry,
Seattle,
Wash.
M
ost dentists delegate the fabrication of framework castings for removable partial dentures to commercial dental laboratories. The work usually is not done under the direct supervision of the dentist because of the geographic separation of the laboratory and the dental office. The work authorization is limited by its two-dimensional aspect and can only describe the work to be done. For instance, the type of clasp prescribed by the dentist may be used, but the length and position of that clasp may be dependent upon the judgment of the dental laboratory technician.
ASSISTING TECHNICIANS WITH EXAMPLE CASTS Many dentists submit an example cast to the technician in addition to the work authorization for framework construction. An example cast has all the elements of the framework drawn on it in the correct proportions and location (Fig. 1) . This cast provides the technician with a three-dimensional view of what the dentist desires and guides him in waxing the framework. The example cast is made by making an additional master cast impression and pouring a second cast. The best cast is used for the master cast. Minor defects in the impression are acceptable for fabrication of the example cast, The dentist must survey the example cast and mark the height of contour in order to draw the components correctly in relation to undercuts. The thickness of the components is still subject to misinterpretation, however, and errors can occur in location of the elements even when an example cast is used.
REVIEWING THE WAX-UP ON THE REFRACTORY CAST Although a failure by the technician to follow the directions provided by the example cast and work authorization must be corrected at the laboratory’s expense, an error will still greatly inconvenience the dentist. The dentist must take the time to remake the final impression and master cast since the original master cast will have been damaged during fabrication of the faulty framework. In addition, the schedule Read
before
*Associate
388
the Pacific Professor,
Coast Department
Society
of Prosthodontists,
of Prosthodontics.
San Diego,
Calif.
for construction of the denture and delay. These problems can master cast with wax blockout especially on completeness and Critiquing the waxed framework lems and helps insure receiving
is disrupted, and this can cause much inconvenience be avoided by having the waxed refractory cast and returned to the dentist for review and modification, placement of the framework components (Fig. 2). when changes still are possible prevents many proba framework that meets the dentist’s expectations.
OBSERVATIONS OF WAXED REFRACTORY CASTS Construction of removable partial denture frameworks at the University of Washington has been delegated to a commercial dental laboratory for several years. The waxed refractory cast and blocked-out master cast are reviewed and corrected prior to casting by the student and his prosthodontic faculty advisor. Records of these observations are available for the last 2 years and are summarized. Each of the evaluations of the 291 refractory casts was assigned to one of four classes according to the most severe error noted, although many casts contained
390
J. Prosthet. Dent.
Frank
Fig. 3. (A) correct. (B) free gingival
April,
1976
The position of the lingual bar as drawn on the master cast by the technician is Inspection of the wax pattern reveals the major connector to be too close to the margins. This error can be corrected easily in the wax-up.
Fig. 4. (A) The dentist has indicated barclasp (A) has been omitted. This loss of time and money for the dentist quickly and easily.
the use of a bar clasp on the example cast. (B) The oversight would have caused much inconvenience and and technician. Additions to the wax pattern are made
several errors. Class I included those wax-ups judged ready to cast without modification; these represented 41 per cent of the observations ( 120 casts). Class II was comprised of 44 wax-ups in which only minor errors were detected. The errors were: ( 1) incorrectly extended or rounded external finish lines (32 casts), (2) improper length or position of the plastic retention (nine casts), and (3) missing tissue rest (three casts). These errors did not seem to jeopardize the final result and accounted for 15 per cent of the total observations. The 59 casts assigned to Class III had an error in the wax-up that was judged serious enough to affect the usefulness of the completed prosthesis. These errors ineluded: ( 1) incorrect position of clasp arms (28 casts), (2) inadequate bulk of clasp arms ( 18 casts), (3) inadequate coverage of guiding planes (eight casts), (4) inadequate length of clasp arms (four casts), and (5) poor post placement in a small edentulous area (one cast). Twenty per cent of the total observations contained at least one of these errors, even though the work authorization was accompanied by an example cast.
Volume
35
Number
4
Evaluating
refractory
cast wax-ups
for dentures
391
Fig. 5. The master cast with wax blockout still present has been oriented on the surveyor at the proper path of insertion. It is obvious that an excessive amount of block-out wax has been used. This error negates the time and effort spent by the dentist in providing guiding planes and results in a loss of retention in the completed denture.
Table
I. Checklist
for reviewing
wax framework
Partial denture component Clasps Rests Major connector Minor connectors Piastic attachment Finish lines
Checklisr None missing; placed into undercut; not lying against the gingival margin; bulk; taper; occlusal clearance None missing; sufficient bulk; occlusal clearance (Note: The technician may prefer to overwax the rests, then finish the metal to proper size.) Bulk; contour; placement Bulk; contour; placement Placement; design; length Sharp to produce a butt joint with the resin; contoured to blend with the denture base
Major errors in the wax-up that would have resulted in an unacceptable casting were placed in Class IV, and these represented 24 per cent of the casts (68 casts ) . The following errors were found in this category: ( 1) too thin or’ narrow major connector (22 casts), (2) incorrectly positioned major connector (20 casts), (3) omission of a rest, clasp, or other component ( 12 casts), (4) use of excessive relief wax (eight casts), (5) use of inadequate or no relief wax (two casts), (6) inadequate bulk of wax for rests (two casts), and (7) use of wrong type of clasp (two casts). Master casts with excessive or inadequate relief were placed in this class because the work had to be redone, It is significant that so many critically important errors were found; this emphasizes the importance of reviewing the waxed refractory cast and blocked-out master cast (Figs. 3 and 4) . REVIEWING
THE WAX
FRAMEWORK
The checklist presented in Table I can be used for reviewing the wax framework. Changes or corrections desired, either in the wax-up or the final metal stage, are noted on the work authorization. The master cast is inspected for the amount of relief wax over the soft-tissue re-
392
J. Prosthet. Dent. April, 1976
Frank
gions, for excessive block-out wax on guiding plane surfaces, and for an unauthorized change in the path of insertion (Fig. 5). A changed path of insertion results in the use of more or less block-out wax in any location than expected. The end result is a casting with less retention and reciprocation than planned. Errors in blocking out the master cast require the technician to make the correction, reduplicate the master cast, rewax the framework, and resubmit them for inspection. These findings should not be interpreted as demeaning of dental laboratory technicians. The laboratory involved has been accredited by the Joint Commission on Accreditation of Dental Laboratories.’ Some dental laboratories will be understandably hesitant to send the cast back to the dentist for review since extra time and some money are involved in this exchange. Also, the dentist must allow an extra day or two in his scheduling sequence for the extra delivery. However, fewer remakes should be experienced, and the dentist will less likely find himself accepting substandard work. The patient is the ultimate beneficiary of this exchange of casts and information which makes the procedure well worthwhile. SUMMARY A review of the waxed refractory cast and blocked-out master cast by the dentist is an effective method for controlling the quality of framework castings. Major errors in wax-ups have been shown to occur frequently, but they are corrected easily if detected prior to casting. This critique can be incorporated readily into the private practice of dentistry. Reference 1.
Dental Laboratories Accredited oratories, J. Am. Dent. Assoc. UNIVERSITY SCHOOL SEATTLE,
OF WASHINGTON OF DENTISTRY WASH.
98195
by the Joint 82: 1423-1429,
Commission 1971.
on Accreditation
of Dental
Lab
refractory
cast wax-ups
for removable
partial
Richard P. Frank, D.D.S., M.S.D.* University
of Washington,
School
of
Dentistry,
Seattle,
Wash.
M
ost dentists delegate the fabrication of framework castings for removable partial dentures to commercial dental laboratories. The work usually is not done under the direct supervision of the dentist because of the geographic separation of the laboratory and the dental office. The work authorization is limited by its two-dimensional aspect and can only describe the work to be done. For instance, the type of clasp prescribed by the dentist may be used, but the length and position of that clasp may be dependent upon the judgment of the dental laboratory technician.
ASSISTING TECHNICIANS WITH EXAMPLE CASTS Many dentists submit an example cast to the technician in addition to the work authorization for framework construction. An example cast has all the elements of the framework drawn on it in the correct proportions and location (Fig. 1) . This cast provides the technician with a three-dimensional view of what the dentist desires and guides him in waxing the framework. The example cast is made by making an additional master cast impression and pouring a second cast. The best cast is used for the master cast. Minor defects in the impression are acceptable for fabrication of the example cast, The dentist must survey the example cast and mark the height of contour in order to draw the components correctly in relation to undercuts. The thickness of the components is still subject to misinterpretation, however, and errors can occur in location of the elements even when an example cast is used.
REVIEWING THE WAX-UP ON THE REFRACTORY CAST Although a failure by the technician to follow the directions provided by the example cast and work authorization must be corrected at the laboratory’s expense, an error will still greatly inconvenience the dentist. The dentist must take the time to remake the final impression and master cast since the original master cast will have been damaged during fabrication of the faulty framework. In addition, the schedule Read
before
*Associate
388
the Pacific Professor,
Coast Department
Society
of Prosthodontists,
of Prosthodontics.
San Diego,
Calif.
for construction of the denture and delay. These problems can master cast with wax blockout especially on completeness and Critiquing the waxed framework lems and helps insure receiving
is disrupted, and this can cause much inconvenience be avoided by having the waxed refractory cast and returned to the dentist for review and modification, placement of the framework components (Fig. 2). when changes still are possible prevents many proba framework that meets the dentist’s expectations.
OBSERVATIONS OF WAXED REFRACTORY CASTS Construction of removable partial denture frameworks at the University of Washington has been delegated to a commercial dental laboratory for several years. The waxed refractory cast and blocked-out master cast are reviewed and corrected prior to casting by the student and his prosthodontic faculty advisor. Records of these observations are available for the last 2 years and are summarized. Each of the evaluations of the 291 refractory casts was assigned to one of four classes according to the most severe error noted, although many casts contained
390
J. Prosthet. Dent.
Frank
Fig. 3. (A) correct. (B) free gingival
April,
1976
The position of the lingual bar as drawn on the master cast by the technician is Inspection of the wax pattern reveals the major connector to be too close to the margins. This error can be corrected easily in the wax-up.
Fig. 4. (A) The dentist has indicated barclasp (A) has been omitted. This loss of time and money for the dentist quickly and easily.
the use of a bar clasp on the example cast. (B) The oversight would have caused much inconvenience and and technician. Additions to the wax pattern are made
several errors. Class I included those wax-ups judged ready to cast without modification; these represented 41 per cent of the observations ( 120 casts). Class II was comprised of 44 wax-ups in which only minor errors were detected. The errors were: ( 1) incorrectly extended or rounded external finish lines (32 casts), (2) improper length or position of the plastic retention (nine casts), and (3) missing tissue rest (three casts). These errors did not seem to jeopardize the final result and accounted for 15 per cent of the total observations. The 59 casts assigned to Class III had an error in the wax-up that was judged serious enough to affect the usefulness of the completed prosthesis. These errors ineluded: ( 1) incorrect position of clasp arms (28 casts), (2) inadequate bulk of clasp arms ( 18 casts), (3) inadequate coverage of guiding planes (eight casts), (4) inadequate length of clasp arms (four casts), and (5) poor post placement in a small edentulous area (one cast). Twenty per cent of the total observations contained at least one of these errors, even though the work authorization was accompanied by an example cast.
Volume
35
Number
4
Evaluating
refractory
cast wax-ups
for dentures
391
Fig. 5. The master cast with wax blockout still present has been oriented on the surveyor at the proper path of insertion. It is obvious that an excessive amount of block-out wax has been used. This error negates the time and effort spent by the dentist in providing guiding planes and results in a loss of retention in the completed denture.
Table
I. Checklist
for reviewing
wax framework
Partial denture component Clasps Rests Major connector Minor connectors Piastic attachment Finish lines
Checklisr None missing; placed into undercut; not lying against the gingival margin; bulk; taper; occlusal clearance None missing; sufficient bulk; occlusal clearance (Note: The technician may prefer to overwax the rests, then finish the metal to proper size.) Bulk; contour; placement Bulk; contour; placement Placement; design; length Sharp to produce a butt joint with the resin; contoured to blend with the denture base
Major errors in the wax-up that would have resulted in an unacceptable casting were placed in Class IV, and these represented 24 per cent of the casts (68 casts ) . The following errors were found in this category: ( 1) too thin or’ narrow major connector (22 casts), (2) incorrectly positioned major connector (20 casts), (3) omission of a rest, clasp, or other component ( 12 casts), (4) use of excessive relief wax (eight casts), (5) use of inadequate or no relief wax (two casts), (6) inadequate bulk of wax for rests (two casts), and (7) use of wrong type of clasp (two casts). Master casts with excessive or inadequate relief were placed in this class because the work had to be redone, It is significant that so many critically important errors were found; this emphasizes the importance of reviewing the waxed refractory cast and blocked-out master cast (Figs. 3 and 4) . REVIEWING
THE WAX
FRAMEWORK
The checklist presented in Table I can be used for reviewing the wax framework. Changes or corrections desired, either in the wax-up or the final metal stage, are noted on the work authorization. The master cast is inspected for the amount of relief wax over the soft-tissue re-
392
J. Prosthet. Dent. April, 1976
Frank
gions, for excessive block-out wax on guiding plane surfaces, and for an unauthorized change in the path of insertion (Fig. 5). A changed path of insertion results in the use of more or less block-out wax in any location than expected. The end result is a casting with less retention and reciprocation than planned. Errors in blocking out the master cast require the technician to make the correction, reduplicate the master cast, rewax the framework, and resubmit them for inspection. These findings should not be interpreted as demeaning of dental laboratory technicians. The laboratory involved has been accredited by the Joint Commission on Accreditation of Dental Laboratories.’ Some dental laboratories will be understandably hesitant to send the cast back to the dentist for review since extra time and some money are involved in this exchange. Also, the dentist must allow an extra day or two in his scheduling sequence for the extra delivery. However, fewer remakes should be experienced, and the dentist will less likely find himself accepting substandard work. The patient is the ultimate beneficiary of this exchange of casts and information which makes the procedure well worthwhile. SUMMARY A review of the waxed refractory cast and blocked-out master cast by the dentist is an effective method for controlling the quality of framework castings. Major errors in wax-ups have been shown to occur frequently, but they are corrected easily if detected prior to casting. This critique can be incorporated readily into the private practice of dentistry. Reference 1.
Dental Laboratories Accredited oratories, J. Am. Dent. Assoc. UNIVERSITY SCHOOL SEATTLE,
OF WASHINGTON OF DENTISTRY WASH.
98195
by the Joint 82: 1423-1429,
Commission 1971.
on Accreditation
of Dental
Lab
