Force activation and biomechanical effects of the Crozat and quad helix appliances in the maxillary mixed dentition.

ABSTRACT

Arch length discrepancy problems have been a longstanding clinical dilemma facing most dentists who treat children. The Crozat appliance has been used in arch development for many years with great success. The quad helix is another appliance that has been utilized with great success in early expansion therapy. The objective of this investigation was to analyze the biomechanical and physical effects of the Crozat appliance when activated for transverse palatal expansion, and to compare these effects with the quad helix appliance. This study used a three-dimensional maxillary photoelastic model in the mixed dentition. Standard Crozat and quad helix appliances were constructed on a working model of the photoelastic maxillary model. The Crozat and quad helix appliances were used to achieve transpalatal expansion in the anterior and posterior quadrants. The stresses transmitted to the supporting structures with each appliance were recorded photographically in the field of a circular polariscope. In addition, each appliance was mounted on a split-stone maxillary cast and the force-activation levels were measured. Transverse palatal expansion was achieved with both appliances at varying adjustments. The stresses generated were localized along the palate, both anteriorly and posteriorly. The forces generated with each appliance suggested more activation of the quad helix appliance was needed to produce a force and resultant effect comparable to that of the Crozat appliance.

INTRODUCTION

Arch length discrepancy problems have been a longstanding clinical dilemma facing most dentists who treat children. A concerned parent will present their child with complaints of "crowded teeth" or "crooked teeth," resulting from arch length deficiency in the corresponding arch. These concerns become evident when the permanent incisors are beginning to erupt into the mouth and demonstrate a lack of adequate space and narrow arch width. McInaney et al. in 1980 stated numerous cases, having been diagnosed with space discrepancy problems in the deciduous and mixed dentitions, have shown great benefits from treatment by early expansion therapy. (1)

The Crozat appliance was introduced by Dr. George B. Crozat in the early 1900's. (2,3) It is a removable appliance made of stainless steel metal that has the mechanical potential to derotate and distalize molars, upright lingually inclined teeth, and expand the arch transversely when properly activated. The philosophy underlying the use of the Crozat appliance is guidance of arch development. (4) This appliance has been used in arch development for many years with great success. (5) The Crozat appliance has been reported to have great versatility and adaptability. (4)

The quad helix appliance is another treatment modality that is widely used in early expansion therapy. It evolved from the fixed "W" arch, with a total of four helical loops incorporated at the anterior and posterior segments of the palate, thus the name "quad helix". (6,7) The helical loops increase the flexibility and the range of force of the appliance by adding 25 mm of wire to the appliance per loop. (6,7) The appliance is constructed of stainless steel wire that is soldered to bands cemented to either the maxillary first permanent molars or the deciduous second molars. It has been successfully utilized in the expansion of the buccal segments and derotation of the banded molars by activating and/or expanding the anterior and palatal arms of the appliance prior to cementation. (7) Research has shown that the quad helix can produce clinical orthopedic effects to the maxilla in children during the mixed dentition, but only dental expansion in adults. (7) With this in mind, the quad helix can be a useful tool in early expansion therapy for a select pediatric patient population.

Many clinicians would prefer to use fixed appliances, such as the quad helix, for transpalatal expansion due to their more predictable results. The Crozat appliance, although it is removable, has been used for many years with great success. (8-10) One of the characteristics of the Crozat appliance is its effective clasp modification. (3) This clasp modification transforms the removable Crozat appliance to provide the necessary retention to resemble fixed appliances. While there has been considerable clinical success utilizing these appliances in the mixed dentition, their force mechanics have not been extensively studied. The purpose of this investigation is to analyze the biomechanical and physical effects of the Crozat appliance when activated for transverse palatal expansion, and to compare these effects with the quad helix appliance.

MATERIALS AND METHODS

A three-dimensional anatomic maxillary model was constructed with photoelastic materials from a pretreatment clinical model of an early mixed dentition with deficient arch length. Different photoelastic materials were used to represent the teeth (PLM-1, Photoelastic Division, Measurements Group, Raleigh, NC) and bony structure of the midface (Solithane-C113-300, Uniroyal Chemical Co., Inc., Middlebury, CT).

Standard Crozat with no auxilliaries and standard quad helix appliances were constructed by Ortek Orthodontic Laboratory (Duarte, CA) on a working model of the photoelastic maxillary model (Figure 1) The Crozat appliance was made with 0.040 in. round stainless steel wire (REF 211-400, 3M Unitek, Monrovia, CA) for the body and buccal extensions. The lingual arms and occlusal rests were made from 0.030 in. round yellow Elgiloy wire (Ductile, E00207, Rocky Mountain Orthodontics, Denver, CO). The cribs and crescents were constructed using round stainless steel wire (0.028 in., Item # 015-410/7, Pozzi Dental Products, Oxnard, CA). These wires were welded with silver solder (Braze 560, Lucas-Milhaupt, Inc., Cudahy, WI).

[FIGURE 1 OMITTED]

The Quad Helix appliance (Fig 2). was constructed with 0.036 in round stainless steel wire for the body wire, and stainless steel bands (3M Unitek, Monrovia, CA) were fitted to the maxillary permanent first molars. These materials were also soldered with silver solder (Braze 560).

[FIGURE 2 OMITTED]

The Crozat and quad helix appliances were used to achieve transpalatal expansion in the anterior and posterior regions. The Crozat appliance was adjusted for 2 mm of anterior and posterior expansion, while the quad helix appliance was adjusted in subsequent increments to provide 2, 4, 6 and 8 mm of anterior and posterior expansion. The Crozat appliance was activated for transpalatal expansion by rotating the right and left cribs distally away from the body of the appliance enough to expand the lingual arms 1 mm on each side for anterior expansion. The midpalatal body wire was then activated to accomplish 2 mm of posterior transpalatal expansion. The quad helix was also activated for transpalatal expansion by adjusting both of the lingual arms to give anterior expansion while the anterior midpalatal body wire was activated for posterior expansion. Each expansion adjustment was measured with a Boley gauge to allow for equal activation of both the right and left sides. The stresses that were transmitted to the supporting structures with each appliance were recorded using digital photography (Nikon D1X, Nikon, Tokyo, Japan) in the field of a circular polariscope (Figure 3). The appliances were photographed before and after each activation, and repeated twice to ensure reproducibility.

[FIGURE 3 OMITTED]

Photoelastic stress analysis was used to analyze and compare the biomechanical effects of each appliance. This photoelastic technique provides a visual evaluation of the internal stresses that are produced as a result of forces being applied to a model of complex structure. Color patterns are produced by the internal stresses which are revealed by a polariscope. (11) The polariscope is comprised of two main elements, the polarizing filters and a light source as seen in Figure 3. The color patterns occur as a result of the alteration of two waves of the polarized light that traveled at different velocities. (11)

In addition, each appliance was then mounted on a split-stone maxillary cast, (Figure 4), and the force-activation levels were measured on a straining frame with a calibrated load-sensing cell (GM2 Universal Transducing Cells, Camarillo, CA). One portion of the cast was fixed to the load cell and the other was clamped to the fixed crosshead of the straining frame. Loads were monitored by a digital read-out after signal treatment using a strain gauge conditioner (models 2130 and 2120A; Measurements Group, Instruments Division, Raleigh, NC). The resulting force from each increment of activation was recorded. Each activation was repeated five times.

[FIGURE 4 OMITTED]

RESULTS

Photoelastic Analysis

Prior to any manipulation of the photoelastic model, examination of the model was performed with the circular polariscope. The model revealed a stress free or minimally inherent stress condition. Therefore, the stress patterns produced in the model after activation of the appliances reflect the effects of the forces generated.

The stress distributions observed in the occlusal view of the maxillary dental arch with the Crozat (Fig. 5A) and Quad Helix (Fig. 5B) appliances activated a total of 2 mm are shown in Figures. These figures revealed the stress patterns produced with the Crozat appliance when activated for 2 mm of expansion were much higher and more concentrated than the stress patterns generated with 2 mm of expansion with the quad helix appliance. The occlusal views of additional activations of the Quad Helix appliance to 4, 6, and 8 mm are shown in Figures 6A through 6C. The additional activations of the quad helix appliance yielded a gradual increase in the intensity of the stress patterns produced. The 8 mm activation revealed concentrated stress patterns similar to that shown by the Crozat appliance when activated for 2 mm of expansion.

[FIGURES 5-6 OMITTED]

Upon further evaluation of the occlusal figures, the stress patterns produced by the transpalatal activation of the Crozat appliance were uniformly distributed in the anterior and posterior palatal areas. The quad helix appliance initially revealed concentrated stress patterns in the posterior palatal region, and as the activation was increased to 6 and 8mm, the anterior palatal stress patterns gradually became more concentrated.

Force-Activation

Comparisons were made between the Crozat and Quad Helix appliances evaluating their force activation characteristics. The results are demonstrated in graphic form as seen in Figure 7. The Crozat appliance activated 2 mm resulted in a force of 530 gm, while the Quad Helix activated at 2 mm produced a force of 110 gm. The data produced for the quad helix appliance is represented as a linear function. The incremental expansion of the Quad Helix appliance from 2 to 8 mm yielded a gradually increasing force, which resulted in a less overall maximum force when compared to the Crozat appliance. The overall maximum force generated with the quad helix appliance at 8 mm of activation was 450 gm, compared to 530 gm produced by 2 mm activation with the Crozat appliance.

[FIGURE 7 OMITTED]

DISCUSSION

The objective of this study was to analyze the biomechanical and physical effects of the Crozat appliance when activated for transverse palatal expansion, and to compare these effects with the biomechanical and physical characteristics of the Quad Helix appliance.

Photoelastic Analysis

Research is lacking in the area of biomechanics of the Crozat appliance. Most of the research performed with the Crozat appliance addresses case reports and clinical discussions. In this study, interpretation of the stress characteristics of the Crozat appliance observed in the photoelastic model is similar to that reported for other removable appliances. (6) With 2 mm activation of the Crozat appliance, the stress patterns produced intense concentrated stresses as demonstrated by the color fringes. Color fringes seen in the photoelastic effect are proportional to the applied loads. Therefore, as the color bands gradually narrow and increase in number, the intensity of the stresses produced also increases and becomes more concentrated.

Literature has shown that the quad helix appliance primarily affects the alveolar bone surrounding the posterior teeth, especially around the banded teeth, with increasing stress patterns observed in this area with incremental activation of the appliance. (6) At 2 mm activation, there are barely any recognizable stress fringes, but at 4 mm, the posterior palate demonstrates obvious stresses. By the 6 and 8 mm activation, much of the palate shows stress patterns, as well as the anterior region which is similar to the 2 mm activation of the Crozat appliance.

Force-Activation

The physical effects of each of these appliances were evaluated by their force activation characteristics. The forces resulting from the activation of a Crozat appliance havw not been reported in the literature. The usual amount of clinical expansion is 1-2 mm. It was surprising to learn that a mere 2 mm activation of the appliance resulted in 530 gm of force. These findings demonstrate the ability to apply a high force level over a short range of activation.

The Quad Helix, on the other hand, produced a very light, continuous force at the 2 mm activation, quantified at only 110 gm. The subsequent incremental increases in the activation resulted in data that produced a linear function as seen in figure 7, reproducing a force activation curve consistent with the data reported by Chaconas and Caputo. (6) Even at the 8 mm activation, which corresponds to the usual amount of clinical expansion of half the bucco-lingual crown distances of deciduous or permanent first molars, it did not reach the value observed in the Crozat appliance. This is consistent with the data presented by Bench, (12) Hermanson et al., (13) and Ranta. (14) These findings demonstrate the increase in flexibility and range of force of the quad helix appliance due to the addition of the helical loops as stated by Chaconas and Caputo. (6,7)

CONCLUSIONS

The biomechanical and physical characteristics of the Crozat and Quad Helix appliances when activated for transverse palatal expansion were determined by photoelastic stress analysis and force activation. The findings reveal the following conclusions from this investigation:

1. It was shown that a standard Crozat appliance can effectively generate force levels for transpalatal expansion similar to or greater than that seen with the quad helix appliance.

2. The Crozat appliance demonstrated higher forces with a short range of action, while the quad helix appliance demonstrated lighter forces over a long range of action.

The authors would like to thank the AAGO and its membership for their support of this project.

REFERENCES

(1) McInaney JB, Adams RM, Freeman M. A nonextraction approach to crowded dentitions in young children: early recognition and treatment. J Am Dent Assoc 1980; 101: 251-7.

(2) White WO, Clark JT. The Crozat removable appliance. Int J Orthod 1976; 14: 6-13.

(3) Proffit WR, Fields HW. Fixed and removable appliance. In: Profit WR, Fields HW, editors. Contempory Orthodontics. 3rd ed, St. Louis: Mosby; 2000: 364-84.

(4) Wiebrecht AT. The philosophy underlying the use of the Crozat appliance. Int J Orthod 1975; 13: 14-5.

(5) Sheppe JH. The construction and use of a Crozat appliance. Int J Orthod 1971; 9: 192-201.

(6) Chaconas SJ, Caputo AA. Observation of orthopedic force distribution produced by maxillary orthodontic appliances. Am J Orthod 1982; 82: 492-501.

(7) Chaconas SJ, de Alba y Levy JA. Orthopedic and orthodontic applications of the quad-helix appliance. Am J Orthod 1977; 72: 422-428.

(8) Owen AH. Crozat treatment. J Clin Orthod 1985; 19: 109-27.

(9) Taylor WH. Crozat principles and technique. J Clin Orthod 1985; 19: 429-41.

(10) Sakabe J, Caputo AA, Nakajima I, Sack CJ. Biomechanical Effects of the Crozat Appliance Compared to the Transpalatal Arch. Pending Publication.

(11) Caputo AA, Standlee JP. Biomechanics in Clinical Dentistry. Chicago: Quintessence; 1987: 21-7.

(12) Bench RW. The Quad Helix Appliance. Seminars in Orthodontics 1998; 4(4): 231-237.

(13) Hermanson H et al. Treatment of unilateral posterior crossbite with quad-helix and removable plate. A retrospective study. Eur J Orthod 1985; 7: 97-102.

(14) Ranta R. Treatment of unilateral posterior crossbite: comparison of the quad-helix and removable plate. J Dent Child 1988; 2: 102-104.

(15) Marasa F. Crozat appliance treatment of buccal crossbite. J Clin Orthod 2003; 37: 329-34.

(16) Hitchcock HP. Pitfalls of the Crozat appliance. Am J Orthod 1972; 62: 461-8

(17) Devos JB. The mechanics of comparative force application in Crozat appliance therapy. J Maxillofac Orthop 1969; 2: 14-20

Diane Colter, DDS, Eunah Cho, DDS, Angelo A. Caputo, and Conrad J. Sack

Diane Colter, DDS, Resident, Department of Pediatric Dentistry, UCLA School of Dentistry, Los Angeles, CA. 90095-1668, Phone: [phone], Fax: [phone], e-mail: [e-mail]

Eunah Cho, DDS, Resident, Department of Pediatric Dentistry, UCLA School of Dentistry, Los Angeles, CA. 90095-1668, Phone: [phone], Fax: [phone], email: [e-mail]

Angelo A. Caputo, PhD, Professor and Chairman, Department of Biomaterials Science, UCLA School of Dentistry. Box 951668, 23-082 CHS, Los Angeles, CA 90095-1668, Phone: [phone], Fax: [phone], email: [e-mail]

Conrad J. Sack, DMD, MS, Lecturer, Department of Pediatric Dentistry and Orthodontics, UCLA School of Dentistry. Los Angeles, CA 90095-1668, Phone: [phone], Fax: [phone], e-mail: [e-mail]