EFFICACY OF TEMPORARY FIXED RETENTION FOLLOWING ...
EFFICACY OF TEMPORARY FIXED RETENTION FOLLOWING ... EFFICACY OF TEMPORARY FIXED RETENTION FOLLOWING ...
1 mm expansion of the intermolar width provides only a 0.25 mm increase in arch perimeter. De La Cruz et al. (1995) evaluated records of 45 Class I patients and 42 Class II, division 1 patients to evaluate the long-term stability of orthodontically induced change in arch form. Dental casts were analyzed at pretreatment, posttreatment and a minimum of 10 years posttreatment. These researchers concluded that arch form tends to return toward its pretreatment shape and that the patient’s pretreatment arch form appears to be the best guide to future stability. Although the researchers found a positive correlation between degree of treatment arch change and degree of posttreatment relapse, they claimed that minimizing treatment arch form change was no guarantee of postretention stability. Vaden, Harris and Gardner (1997) quantified changes in tooth relationships in a sample of 36 extraction patients at 6 years and again at 15 years posttreatment. Although the maxillary intercanine width was expanded more than the mandibular intercanine width during treatment, both arches were expanded slightly, but to a statistically significant extent. An interesting observation noted during this study was that with any study of this type, “it is difficult to determine whether intercanine ‘expansion’ occurred by a transverse movement of the teeth or retraction of the canines in to the premolar extraction spaces, a broader part of the arch” (p 545). Posttreatment results indicated that a significant amount of the maxillary expansion was maintained, while half of the expansion that occurred in the mandible during treatment was lost. Maxillary and mandibular arch length was reduced an average of 5.7 mm during treatment as a result of tooth extraction, but it also continued to decrease an average of 1 mm throughout the two recall periods even though no spacing was left following active treatment. This continued reduction in arch length was attributed to the mesial migration of teeth in the buccal segment. Both arches become shorter and narrower with age. These results reiterate the conclusions of previous researchers who found that posttreatment arch dimension changes and dental crowding can be minimized and kept similar to changes seen in untreated samples by maintaining pretreatment arch dimension and keeping alterations in the intermolar and intercuspid distances to a minimum during treatment (Steadman 1961; Lundström 1968; Glenn et al. 1987; Bishara et al. 1989). Burke et al. (1998) applied a meta-analysis technique of literature review to a total of 26 studies to assess the longitudinal stability of posttreatment mandibular intercanine width. Glass (1976, p 3) defines meta-analysis as “the statistical analysis of a large collection of results from individual studies for the purpose of integrating findings.” Weighted averages and standard deviations for the means of 1,233 patients were analyzed for changes in intercanine width at 9
three time intervals: during treatment, immediately following treatment, and after removal of all retention. Regardless of pretreatment molar classification or whether treatment involved extractions, mandibular intercanine width was found to expand during treatment by 0.8 to 2.0 mm. However, at posttreatment, the mandibular intercanine width constricted by 1.2 to 1.9 mm and showed a net change in posttreatment on the order of from 0.5 mm expansion to 0.6 mm constriction. The results of this meta-analysis support the concept of maintenance of the original intercanine width during orthodontic treatment. In conclusion, the literature suggests that maintaining the patient’s existing arch dimensions, with the possible exceptions of patients who exhibit malformed or mutilated arches, results in the most stable posttreatment results. There is also a direct correlation with the ability to maintain arch dimension and tooth extraction. Historically, orthodontists were left with only two treatment alternatives when faced with a crowded dental arch: either expansion of the arch or tooth extraction. Lindauer (1997) emphasized that when considering extraction of teeth, other contributing factors should be evaluated in addition to intra-arch crowding. These include “the predicted effect of treatment on lip protrusion, the amount of overbite present, the patient’s periodontal condition, and whether or not there are missing or compromised teeth” (p 31). For each millimeter of incisor advancement or flaring, the arch perimeter is increased by 2 mm (Ricketts et al. 1982; Lindauer 1997). In addition, arch width increases are possible but the space yielded is smaller for any given amount of expansion (Ricketts et al. 1982; Germane et al. 1991; Lindauer 1997). The literature review suggests that arch dimension changes resulting from treatment modalities such as minor arch expansion and minimal incisor flaring can be successfully utilized in patients exhibiting mild crowding without substantially diminishing posttreatment stability. However, in cases with moderate to severe space requirements, such as severe dental crowding or anterior protrusion cases, where excessive arch expansion or incisor flaring would be necessary to relieve the tooth-arch discrepancies, tooth extraction continues the be the most appropriate treatment modality to best allow for predictable arch dimension maintenance and thus prolonged posttreatment stability. Occlusion and Posttreatment Tooth Position The establishment of a functional and stable posttreatment occlusion should be a primary objective of orthodontic treatment. Kingsley (1880, p 63) stated, “The occlusion of the teeth is the most potent factor in determining the 10
- Page 1 and 2: EFFICACY OF TEMPORARY FIXED RETENTI
- Page 3 and 4: DEDICATION This thesis is dedicated
- Page 5 and 6: ABSTRACT Instability of the occlusi
- Page 7 and 8: CHAPTER 5. DISCUSSION .............
- Page 9 and 10: LIST OF FIGURES Figure 3-1. All cas
- Page 11 and 12: Figure 4-14. Box plot of the distri
- Page 13 and 14: Joondeph and Riedel (1994, p 908) d
- Page 15 and 16: Strang (1952, p 794) claimed that
- Page 17 and 18: malocclusion must be maintained if
- Page 19: e aimed at maintaining, in most ins
- Page 23 and 24: mechanical treatment does not neces
- Page 25 and 26: elation, the masticatory system wil
- Page 27 and 28: exerted on the denture from the buc
- Page 29 and 30: In summary, the variance in tongue
- Page 31 and 32: Sinclair and Little (1983, p 114) a
- Page 33 and 34: Study and 43 orthodontically treate
- Page 35 and 36: and Sakols 1982; Vaden et al. 1997;
- Page 37 and 38: years postretention. Årtun et al.
- Page 39 and 40: adjustment, if necessary. This abil
- Page 41 and 42: Duration of Retention The premise i
- Page 43 and 44: The reduction in tooth structure of
- Page 45 and 46: 4. The most stable position of the
- Page 47 and 48: CHAPTER 3. MATERIALS AND METHODS Sa
- Page 49 and 50: The present sample consisted of the
- Page 51 and 52: Figure 3-2. Illustration of how mol
- Page 53 and 54: Figure 3-3. Illustration showing di
- Page 55 and 56: Figure 3-5. Illustration showing mi
- Page 57 and 58: Figure 3-6. Illustration showing an
- Page 59 and 60: Figure 3-8. Illustration showing in
- Page 61 and 62: 34. LR3 cusp tip point. 35. Right d
- Page 63 and 64: Figure 3-10. Illustration showing o
- Page 65 and 66: Figure 3-11. Illustration of Inciso
- Page 67 and 68: 3. Go, Gonion (anatomic): The most
- Page 69 and 70: Figure 3-13. Depiction of the angle
three time intervals: during treatment, immediately following treatment, and<br />
after removal of all retention. Regardless of pretreatment molar classification or<br />
whether treatment involved extractions, mandibular intercanine width was<br />
found to expand during treatment by 0.8 to 2.0 mm. However, at posttreatment,<br />
the mandibular intercanine width constricted by 1.2 to 1.9 mm and showed a net<br />
change in posttreatment on the order of from 0.5 mm expansion to 0.6 mm<br />
constriction. The results of this meta-analysis support the concept of<br />
maintenance of the original intercanine width during orthodontic treatment.<br />
In conclusion, the literature suggests that maintaining the patient’s<br />
existing arch dimensions, with the possible exceptions of patients who exhibit<br />
malformed or mutilated arches, results in the most stable posttreatment results.<br />
There is also a direct correlation with the ability to maintain arch dimension and<br />
tooth extraction. Historically, orthodontists were left with only two treatment<br />
alternatives when faced with a crowded dental arch: either expansion of the arch<br />
or tooth extraction. Lindauer (1997) emphasized that when considering<br />
extraction of teeth, other contributing factors should be evaluated in addition to<br />
intra-arch crowding. These include “the predicted effect of treatment on lip<br />
protrusion, the amount of overbite present, the patient’s periodontal condition,<br />
and whether or not there are missing or compromised teeth” (p 31). For each<br />
millimeter of incisor advancement or flaring, the arch perimeter is increased by 2<br />
mm (Ricketts et al. 1982; Lindauer 1997). In addition, arch width increases are<br />
possible but the space yielded is smaller for any given amount of expansion<br />
(Ricketts et al. 1982; Germane et al. 1991; Lindauer 1997).<br />
The literature review suggests that arch dimension changes resulting from<br />
treatment modalities such as minor arch expansion and minimal incisor flaring<br />
can be successfully utilized in patients exhibiting mild crowding without<br />
substantially diminishing posttreatment stability. However, in cases with<br />
moderate to severe space requirements, such as severe dental crowding or<br />
anterior protrusion cases, where excessive arch expansion or incisor flaring<br />
would be necessary to relieve the tooth-arch discrepancies, tooth extraction<br />
continues the be the most appropriate treatment modality to best allow for<br />
predictable arch dimension maintenance and thus prolonged posttreatment<br />
stability.<br />
Occlusion and Posttreatment Tooth Position<br />
The establishment of a functional and stable posttreatment occlusion<br />
should be a primary objective of orthodontic treatment. Kingsley (1880, p 63)<br />
stated, “The occlusion of the teeth is the most potent factor in determining the<br />
10
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