The importance of making and retaining diagnostic casts

John O. Grippo, DDS, FACD

Gordon J. Christensen, DDS, MSD, PhD

The objective of this paper is to stress the significance of making and retaining conventional diagnostic stone casts of a patient's mandible, maxilla, teeth, and the surrounding tissues. Full-arch diagnostic casts are valuable tools in determining various physiological and morphological changes that take place during the life span of the jaws, teeth, and periodontal tissues (Figs. 1-5).

Digital imaging impressions can also be used to make extremely accurate stone casts, which reproduce the jaws, teeth, gingival tissues, and palatal area (Fig. 6).^1-4 Though the intraoral digital scanners are moving rapidly into the profession, use of conventional materials remain the most common source for making impressions. Stone casts are familiar to practitioners and, at this time, provide precise information on the bone, tissues surrounding the teeth, as well as their morphology and position. Use of stone casts can be an effective means of patient education, as they provide comparable observation of the changes that have taken place over time in the position and anatomy of teeth, bone, and soft tissues. A few noteworthy examples are demonstrated in Figs. 1-5.

Diagnostic casts are valuable for research purposes and forensic information as they provide observable, precise geometry of the teeth and jaws.

Occlusion constantly changes, and comparison of the changes on stone casts provide valuable information to the practitioner and can be used to educate the patient.⁵

Fig. 1: The noncarious lesions on Nos. 9 through 11 as seen in the above photograph are more visible and demonstrable to the patient by using diagnostic casts. Note that the geometry of the lesions on Nos. 9 through 11 are more distinct than in the photograph.

Fig. 2: Diagnostic casts clearly depicting the progression of noncarious facial lesions within the enamel caused by acidic biocorrosion,⁶ toothbrush abrasion, and stress-induced abfractions on the facial of Nos. 22 through 25.⁷Occlusal wear facets from bruxism can be noted and correspond to the enlarging facial lesions.

Fig. 3: Diagnostic casts demonstrating the enlargement of mandibular tori and occlusal facets, which appear to be related to bruxism. Both tori were removed (right photo) in 1986 and subsequently recurred. cf. Fig. 4.

Occlusion changes are caused by:

• Tooth extraction without subsequent restorative dentistry

• Differential wear of restorative materials

• Caries on the occlusal and interproximal surfaces

• Parafunction

• Periodontal disease

• Iatrogenic dentistry

• Orthodontic treatment

• Proximal wear of teeth

• Traumatic accidents

• Skeletal growth differences

• Pathological skeletal changes

Fig. 4: Diagnostic cast demonstrating the recurrent growth of both mandibular tori following their removal in 1986 as depicted in Fig. 5. Note the increase size of the facets on the bicuspids and cuspids from the 1974 and 1986 casts. The lower right first bicuspid is an acrylic face crown showing wear from bruxism and toothbrushing.

Fig. 5: Sequential casts demonstrating the absence of tori in 1939, and the recurrence and growth of tori following removal in 1986. Note that the facets correspondingly enlarged over time from 1974 through 1990. This figure relates to the photos in Figs. 3 and 4.

Fig. 6: Digital casts of a Class 2, Div. 1 treated with six months of cross bow Class 2 corrector followed by a 12-month fixed appliance. 3-D casts from iTero scan.

It is advisable that dentists, especially orthodontists, make and retain casts following completion of patient treatment, and that they recall their patients to monitor changes in occlusion and other structures.Each state has a regulatory board of examiners that has guidelines as to the retention of diagnostic casts. Orthodontists in most states are required to retain diagnostic casts for seven years. In addition to retaining the patient's records, casts relating to prosthetic replacements such as crowns, bridges, and implants may be required to be retained for seven years. In order to conform to the laws of the board of examiners, dentists should be aware of these rules governing the retention of casts in their respective states. If storage of the casts presents a problem, the patient can be asked to store them and be advised of their importance for future possible changes.

Listed below are numerous clinical conditions and considerations that can be observed with diagnostic casts.

Diagnostic casts show many tooth characteristics including:

a. Size

b. Shape

c. Length and width

d. Position - e.g., buccal, lingual, mesial, or distal orientation

e. Open contacts

f. Contact points to see signs of interproximal wear caused by friction

g. Marginal ridge positions

h. Missing teeth

i. Occlusal anatomy

j. Rotation of the teeth

k. Signs of bulimia

l. Signs of gastric acid reflux

m. Midline position

n. Cross-bite relationships

o. Interocclusal space

p. Signs of bruxism

q. Class VI lesions - occlusal and incisal invaginations

r. Noncarious cervical lesions (NCCLs) - signs of stress (abfraction), friction, and biocorrosion

s. Areas of attrition

t. Areas of abrasion

u. Personal identification for forensic examinations

v. Degree of occlusal wear

w. Wear facets indicating possible prematurities [prematurities must be confirmed with the patient in centric relation CR/maximum interocclusal position (MIP)]

x. Angle's classification of occlusion

Diagnostic casts provide information on bone characteristics as follows:

a. Tori

b. Exostoses

c. Paget's disease

d. Acromegaly

e. Gingival recession indicating bone loss

Mounted diagnostic casts provide additional information including:

a. Occlusal prematurities

b. Working interferences

c. Balancing interferences

d. Evaluation of group function

e. Evaluation of cuspid guidance

Utilization of diagnostic casts for various procedures

Diagnostic casts for esthetic dentistry:

a. Design of porcelain veneers

b. To determine the need for an occlusal bite guard

c. To determine the amount of tooth reduction

d. To determine the midline

Diagnostic casts for oral surgery:

a. Position of implants

b. Bone - tori, exostoses

c. Width of the ridges

d. Height of the ridges

e. Size of the implant

Diagnostic casts for orthodontics:

a. Occlusal relationship (neutrocclusion, distocclusion, and mesiocclusion)

b. Horizontal overjet and vertical overbite

c. Dental midlines

d. Asymmetries of the dental arches

e. Arch length discrepancies

f. Occlusal plane

g. Tooth size discrepancies

h. Tooth inclination and rotations

i. Skeletal and dental cross-bites

j. Articulated casts mounted in centric relation can determine the presence of a functional mandibular shift or dental interferences

- The eruption and loss of teeth during active growth occasionally results in a prematurity or "fulcrum" that may alter the position of the mandible, thus forcing the patient into a convenient or habitual occlusion. For example, a premature contact on an incline of a posterior tooth may displace the mandible forward into a more anterior relationship, thus creating noticeable discrepancy in CR/ (MIP).

k. Retaining casts for future reference to monitor any changes in occlusion

Diagnostic casts for pediatric dentistry:

a. Malocclusion

b. Skeletal disharmonies

c. Overjet and transverse discrepancies

d. Arch length discrepancies

e. Ectopic eruption of teeth

f. Arch asymmetries

g. Missing teeth

h. Attrition from bruxism

i. Noncarious cervical lesions

Diagnostic casts for periodontics:

a. Flap design and delineation of area to be involved

b. Fabrication of occlusal splints and night guards

c. Position of the gingival margins

d. Evaluation of plunger cusps

e. Crown/root ratio

f. Frenum attachment

Diagnostic casts for fixed prostheses:

a. Occlusal disharmonies

b. Inclinations of teeth

c. Poor position or supereruption of teeth

d. Length of clinical crowns of abutment teeth

e. Mandibular or palatal tori and bony exostoses

f. Necessity for preprosthetic surgery

g. Design of restorations

h. Utilizing casts for future reference as the prostheses serve in the mouth

Diagnostic casts for removable partial prostheses:

a. Design of removable partial denture frameworks

b. Interarch space available

c. Shape of arches

d. Need for surgery to remove bony overgrowths or tori

e. Design and choice of precision attachments

f. Evaluate the position of the lingual bar and its relationship to the lingual and buccal frenum

g. Design of the palatal major connectors

h. Position of the retromolar pad

Diagnostic casts for removable complete prostheses:

a. Interarch space available

b. Presence of undercuts

c. Tori or bony overgrowths

d. Need for preprosthetic surgery

e. Shape and depth of the arches

f. Jaw relations at determined vertical dimension

g. Position of the retromolar pads

h. The presence and development of rugae

Summary

Currently, conventional diagnostic stone casts of patients' jaws provide a valuable resource in providing information for the optimum care of teeth, bones, and soft tissues. Digital casts are now being used by many practitioners and will eventually become more common. Numerous considerations have been listed to guide dentists in considering and addressing changes that usually take place over time. When necessary, periodic casts can be made to demonstrate these changes to the patient.

Acknowledgments

The authors wish to thank Brennan Cassidy, BS, Longmeadow, Massachusetts; Linda Rigali, DMD, Northampton, Massachusetts; Kevin Coughlin, DMD, MAGD, MBA, Longmeadow, Massachusetts; Daniel S. Oh, PhD, assistant professor, College of Dental Medicine, Columbia University, New York, New York; Paul H. Rigali, DDS, adjunct associate clinical professor of orthodontics, Henry M. Goldman School of Dentistry, Boston University; and Barbara A.Young, RDH, executive director, Massachusetts Board of Registration for Dentistry, for their contributions to this paper.

References

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John O. Grippo, DDS, FACD, is a retired dentist having practiced for 45 years. He has been an adjunct faculty professor at Western New England University in the Department of Biomedical Engineering for the past 28 years, conducting studies on the dynamics of occlusion, its effects of stress manifested as abfraction, and biocorrosion, a term which he recently redefined.

Gordon J. Christensen, DDS, MSD, PhD, is a practicing prosthodontist in Provo, Utah. He is the founder and director of Practical Clinical Courses, an international continuing-education organization initiated in 1981 for dental professionals. Dr. Christensen is a cofounder (with his wife, Dr. Rella Christensen) and CEO of Clinicians Report (formerly Clinical Research Associates).